Patent Description:
<CIT> discloses a water heater comprising a gas burner being configured to combust gas if a heat demand is present, further comprising a heat exchanger being configured to heat water using the thermal energy provided with the combustion of the gas, further comprising an input pipe being configured to provide water to be heated to the heat exchanger, further comprising an output pipe being configured to provide water heated by the heat exchanger to the at least one water consumer, and further comprising a connecting pipe, namely a bypass pipe, extending between the input pipe and the output pipe. The gas burner comprises a burner chamber in which the combustion of the gas takes place. The gas burner further comprises a gas armature providing the gas to be combusted to the burner chamber. Both, the burner chamber and the gas armature from part of the gas burner.

<CIT>, <CIT> and <CIT> disclose other water heaters according to the prior art.

The gas burner of a water heater, especially the gas armature of the gas burner, needs to be calibrated from time to time. For performing a calibration of the gas burner, the gas burner needs to be operated at a defined calibration burner load for a defined calibration time interval. For water heaters according to the prior art, such a calibration of the gas burner can only be executed when a heat demand is present, namely if heated water is requested by at least one water consumer. Depending on the heat demand of the at least one water consumer, the operation of the gas burner at the defined calibration burner load for the defined calibration time interval can lead to a water temperature at the respective water consumer being either too high or too low. This is a significant disadvantage of water heaters known from prior art.

<CIT> discloses a water heater according vto the preamble of claim <NUM>.

<CIT> and <CIT> disclose other prior art.

Against this background, a novel water heater and methods to operate such a water heater are provided.

The invention provides a water heater according to claim <NUM>.

The water heater comprises a gas burner being configured to combust gas if a heat demand is present, namely if heated water is requested by at least one water consumer.

The water heater further comprises a heat exchanger being configured to heat water using the thermal energy provided with the combustion of the gas, wherein the heat exchanger is a condensing heat exchanger.

The water heater further comprises an input pipe being configured to provide water to be heated to the heat exchanger.

The water heater further comprises an output pipe being configured to provide water heated by the heat exchanger to the at least one water consumer.

The water heater further comprises a siphon or trap being configured to collect condensate resulting at the condensing heat exchanger during operation of the water heater.

The water heater further comprises a first connection pipe and a valve acting together with the first connection pipe, both the first connection pipe and the valve are configured to guide water heated by heat exchanger from the output pipe to the siphon or trap, and/or to guide water not heated by the heat exchanger from the output pipe to the siphon or trap.

The water heater further comprises a second connecting pipe extending between the input pipe and the output pipe.

In a first alternative defined in claim <NUM>, a separate valve acts together with the second connection pipe being configured to guide water from input pipe to the output pipe.

In a second alternative defined in claim <NUM>, the first connecting pipe extends between the second connecting pipe and the siphon or trap. The valve acting together with the first connection pipe is provided by a <NUM>-way-valve connected between the first connecting pipe and the second connecting pipe. Said valve acts also together with the second connection pipe, wherein a first port of the <NUM>-way-valve is connected to the output pipe through a first section of the second connecting pipe, wherein a second port of the <NUM>-way-valve is connected to the input pipe through a second section of the second connecting pipe, and wherein a third port of the <NUM>-way-valve is connected to the siphon or trap through the first connecting pipe. Both, water heated by heat exchanger and water not heated by the heat exchanger can be guided from the output pipe to the siphon or trap through the first connection pipe and the valve acting together with the first connection pipe.

The novel water heater can be operated with the gas burner combusting gas even if there is no heat demand by a water consumer.

Calibrations of the water heater can be executed even if there is no heat demand by a water consumer. The water heated by the water heater during such a calibration can be guided to the siphon or trap.

According to a first embodiment of the first alternative, the valve acting together with the first connection pipe is a <NUM>-way valve positioned within the first connection pipe, wherein a first port of the <NUM>-way-valve is connected to the output pipe through a first section of the first connecting pipe, and wherein a second port of the <NUM>-way-valve is connected to the siphon or trap through a second section of the first connecting pipe. Both, water heated by heat exchanger and water not heated by the heat exchanger can be guided from the output pipe to the siphon or trap through the first connection pipe and the valve acting together with the first connection pipe.

According to a second embodiment of the first alternative, the valve acting together with the first connection pipe is a <NUM>-way valve, wherein a first port of the <NUM>-way-valve is connected to the heat exchanger through a first section of the output pipe, wherein a second port of the <NUM>-way-valve is connected to the at least one water consumer through a second section of the output pipe, and wherein a third port of the <NUM>-way-valve is connected to the siphon or trap through the first connecting pipe. Both, water heated by heat exchanger and water not heated by the heat exchanger can be guided from the output pipe to the siphon or trap through the first connection pipe and the valve acting together with the first connection pipe.

Further on, the invention provides methods to operate a water heater according to claims <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

Preferred developments of the invention are provided by the dependent claims and the description which follows. Exemplary embodiments are explained in more detail on the basis of the drawing, in which:.

<FIG> and <FIG> each show a water heater <NUM>.

The water heater <NUM> comprises a gas burner <NUM> being configured to combust a gas if a heat demand is present, namely if heated water is requested by at least one water consumer <NUM>.

The gas burner comprises <NUM> a burner chamber <NUM>. A burner rod <NUM> of the gas burner <NUM> is positioned within the burner chamber <NUM>.

Gas <NUM> is provided to the burner rod <NUM> for combusting the gas <NUM> within the burner chamber <NUM>. The gas <NUM> is preferably provided as a gas/air mixture <NUM>. The combustion of the gas <NUM> of gas/air mixture <NUM> results into flames <NUM> and exhaust gas <NUM>. The exhaust gas <NUM> emerges from the burner chamber <NUM> through a chimney.

As mentioned above, the gas <NUM> is preferably provided as a gas/air mixture <NUM>. Such a gas/air mixture <NUM> is usually provided by a gas armature <NUM> of the gas burner <NUM>. Such gas armatures <NUM> are well known. Such a gas armature <NUM> usually comprises a fan (not shown) proving a flow of air <NUM>, a gas valve or gas modulator (not shown) providing a flow of the gas <NUM> and a mixing unit (not shown) mixing the air flow with the gas flow. The mixing ratio of gas <NUM> and air <NUM> within the gas/air mixture <NUM> is usually kept at a defined value over the entire modulation rage of the gas burner <NUM> such that at any burner load of the gas burner <NUM> the mixing ratio of the gas/air mixture <NUM> is kept at the defined value.

The water heater <NUM> further comprises a heat exchanger <NUM> being configured to heat water using the thermal energy provided with the combustion of the gas <NUM>. The heat exchanger <NUM> is positioned inside the burner chamber <NUM>. The heat exchanger <NUM> is a condensing heat exchanger.

The water heater <NUM> further comprises an input pipe <NUM> being configured to provide unheated water, namely water to be heated by the heat exchanger <NUM>, to the heat exchanger <NUM>. The water heater <NUM> further comprises an output pipe <NUM> being configured to provide water heated by the heat exchanger <NUM> to the at least one water consumer <NUM>. The water heater <NUM> further comprises a siphon or trap <NUM> being configured to collect condensate resulting at the condensing heat exchanger <NUM> during operation of the water heater <NUM>.

The water heater <NUM> further comprises a first connecting pipe <NUM> and a valve <NUM> acting together with the first connection pipe <NUM>. Both the first connection pipe <NUM> and the valve <NUM> are configured to guide water heated by heat exchanger <NUM> from the output pipe <NUM> to the siphon or trap <NUM>, and to guide water not heated by the heat exchanger <NUM> from the output pipe <NUM> to the siphon or trap <NUM>.

In <FIG> and <FIG>, the first connection pipe <NUM> extends between the output pipe <NUM> and the siphon or trap <NUM>. The valve <NUM> acting together with the first connection pipe <NUM> is a <NUM>-way valve positioned within the first connection pipe <NUM>, wherein a first port 23a of the <NUM>-way-valve is connected to the output pipe <NUM> through a first section 21a of the first connecting pipe <NUM>, and wherein a second port 23b of the <NUM>-way-valve is connected to the siphon or trap <NUM> through a second section 21b of the first connecting pipe <NUM>. <FIG> according to a first embodiment of the invention shows a modification of water heater <NUM> of <FIG>. In <FIG> the water heater <NUM> comprises further a second connecting pipe <NUM> extending between the input pipe <NUM> and the output pipe <NUM>, and a separate valve <NUM> acting together with the second connection pipe <NUM> being configured to guide water from input pipe <NUM> to the output pipe <NUM>. A first section 20a of the second connecting pipe <NUM> extends between the output pipe <NUM> and the separate valve <NUM>. A second section 20a of the second connecting pipe <NUM> extends between the input pipe <NUM> and the separate valve <NUM>. All other details of the water heater of <FIG> are identical to the water heater of <FIG>. The second connecting pipe <NUM> may also be called bypass pipe.

If a heat demand is present at the water heater <NUM> of <FIG> and <FIG>, namely if heated water is requested by the at least one water consumer <NUM>, the input pipe <NUM> provides water to the heat exchanger <NUM>, said water becomes heated by the heat exchanger <NUM> when flowing through the same using the thermal energy resulting from the combustion of the gas <NUM> by the gas burner <NUM>, and the water heated by the heat exchanger <NUM> is provided to the respective water consumer <NUM>. In this situation the valve <NUM> is closed. In <FIG> the valve <NUM> may be opened or closed in this situation. If the valve <NUM> is closed in this situation, only water heated by the heat exchanger <NUM> is provided to the respective water consumer <NUM>. If the valve <NUM> is opened in this situation, the water heated by the heat exchanger <NUM> becomes mixed with unheated water bypassing the heat exchanger <NUM> and said mixture is provided to the respective water consumer <NUM>. If a heat demand is not present at the water heater <NUM> of <FIG> and <FIG>, namely if heated water is not requested by the at least one water consumer <NUM>, the gas burner <NUM> may be active and may combust gas <NUM> or may inactive and may not combust gas <NUM>.

If a heat demand is not present and if the gas burner <NUM> of the water heater <NUM> of <FIG> and <FIG> is combusting gas <NUM>, water heated by the heat exchanger <NUM> can be provided to the siphon or trap <NUM> from the output pipe <NUM> through the first connecting pipe <NUM> and through the valve <NUM>.

If a heat demand is not present and if the gas burner <NUM> of the water heater <NUM> of <FIG> and <FIG> is not combusting gas <NUM>, water not being heated by the heat exchanger <NUM> but flowing through the same can be provided to the siphon or trap <NUM> from the output pipe <NUM> through the first connecting pipe <NUM> and through the valve <NUM>.

So, heated water as well as unheated water can be provided to the siphon or trap <NUM> without any water consumption at a water consumer <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a calibration of the gas burner <NUM> of the water heater <NUM> of <FIG> and <FIG>, the water heater <NUM> is operated as follows: The gas burner <NUM> is operated at a defined calibration burner load for a defined calibration time interval and the water heated by the heat exchanger <NUM> during the calibration is provided by the valve <NUM> to the siphon or trap <NUM>. During the calibration, the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>, namely in such a way that the heated water flows from the output pipe <NUM> through the first section 21a of the first connecting pipe <NUM>, through the valve <NUM> and through the second section 21b of the first connecting pipe <NUM> to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a filling the siphon or trap <NUM> directly after installation of the water heater <NUM> of <FIG> and <FIG>, the water heater <NUM> is operated as follows: Unheated water or heated water is provided by the valve <NUM> to the siphon or trap <NUM>. Preferably, the unheated water or the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>.

To provide heated water to the siphon or trap <NUM>, the gas burner <NUM> is combusting gas <NUM> at a defined burner load. To provide unheated water to the siphon or trap <NUM>, the gas burner <NUM> is not combusting gas <NUM>. The heated water or the unheated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>, namely in such a way that the water flows from the output pipe <NUM> through the first section 21a of the first connecting pipe <NUM>, through the valve <NUM> and through the second section 21b of the first connecting pipe <NUM> to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a cleaning the siphon or trap <NUM> the water heater <NUM> of <FIG> and <FIG> is operated as follows: Unheated water or heated water is provided by the valve <NUM> to the siphon or trap <NUM>. Unheated water or heated water is provided by the valve <NUM> to the siphon or trap <NUM>. Preferably, the unheated water or the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a descaling of the heat exchanger <NUM> the water heater <NUM> of <FIG> and <FIG> is operated as follows. The following steps i) and ii) are alternately executed. Step i): Combust gas with the gas burner <NUM> at a defined burner load for a defined first time interval and provide the heated water to the siphon or trap <NUM>. Step ii): Stop combustion of gas within the gas burner <NUM> for a defined second time interval and provide the unheated water to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a descaling of the heat exchanger <NUM> the water heater <NUM> of <FIG> and <FIG> is alternatively operated as follows. The following steps i) and ii) are alternately executed. Step i): Combust gas with the gas burner <NUM> at a defined first burner load for a defined first time interval and provide the heated water to the siphon or trap <NUM>. Step ii) combust gas with the gas burner <NUM> at a defined second burner load for a defined second time interval and provide the heated water to the siphon or trap <NUM>, wherein the first burner load is relatively low compared to the second burner load. The first burner load may be a minimum burner load and the second burner load may be a maximum burner load.

For the descaling of the heat exchanger <NUM> of the water heater <NUM>, during the first time interval and during the second time interval the water is provided from the output pipe <NUM> to the siphon or trap <NUM> through the valve <NUM>, namely in such a way that the water flows from the output pipe <NUM> through the first section 21a of the first connecting pipe <NUM>, through the valve <NUM> and through the second section 21b of the first connecting pipe <NUM> to the siphon or trap <NUM>.

If in <FIG> and <FIG> water flows from output pipe <NUM> to the siphon or trap <NUM>, the valve <NUM> is opened.

<FIG> and <FIG> both show a water heater <NUM>. The comparative water heater of <FIG> differs from the comparative water heater of <FIG> and the water heater of <FIG> according to a second embodiment of the invention differs from the water heater of <FIG> according the first embodiment of the invention merely by the design of the respective valve <NUM>, <NUM> acting together with first connection pipe <NUM>. While in <FIG> and <FIG> said valve <NUM> is provided by a <NUM>-way-valve, in <FIG> and <FIG> said valve <NUM> is provided by a <NUM>-way-valve. In <FIG> and <FIG>, a first port 25a of the <NUM>-way-valve is connected to the heat exchanger <NUM> through a first section 19a of the output pipe <NUM>, wherein a second port 25b of the <NUM>-way-valve is connected to the at least one water consumer <NUM> through a second section 19b of the output pipe <NUM>, and wherein a third port 25c of the <NUM>-way-valve is connected to the siphon or trap <NUM> through the first connecting pipe <NUM>.

<FIG> differs from <FIG> merely by the second connecting pipe <NUM> extending between the input pipe <NUM> and the output pipe <NUM>, and by the separate valve <NUM> acting together with second connection pipe <NUM> being configured to guide water from input pipe <NUM> to the output pipe <NUM>.

In <FIG> and <FIG> as well as in <FIG> and <FIG> both the first connection pipe <NUM> and the respective valve <NUM>, <NUM> are configured to guide water heated by heat exchanger <NUM> from the output pipe <NUM> to the siphon or trap <NUM>, and to guide water not heated by the heat exchanger <NUM> from the output pipe <NUM> to the siphon or trap <NUM>. The second connecting pipe <NUM> may also be called bypass pipe.

If a heat demand is present at the water heater <NUM> of <FIG> and <FIG>, namely if heated water is requested by the at least one water consumer <NUM>, the input pipe <NUM> provides water to the heat exchanger <NUM>, said water becomes heated by the heat exchanger <NUM> when flowing through the same using the thermal energy resulting from the combustion of the gas <NUM> by the gas burner <NUM>, and the water heated by the heat exchanger <NUM> is provided to the respective water consumer <NUM>. In this situation the ports 25a, 25b of the valve <NUM> are opened and the port 25c of the valve <NUM> is closed. In <FIG> the valve <NUM> may be opened or closed in this situation. If the valve <NUM> is closed in this situation, only water heated by the heat exchanger <NUM> is provided to the respective water consumer <NUM>. If the valve <NUM> is opened in this situation, the water heated by the heat exchanger <NUM> becomes mixed with unheated water bypassing the heat exchanger <NUM> and said mixture is provided to the respective water consumer <NUM>. If a heat demand is not present at the water heater <NUM> of <FIG> and <FIG>, namely if heated water is not requested by the at least one water consumer <NUM>, the gas burner <NUM> may be active and may combust gas <NUM> or may inactive and may not combust gas <NUM>.

If a heat demand is not present and if the gas burner <NUM> of the water heater <NUM> of <FIG> and <FIG> is not combusting gas <NUM>, water not being heated by the heat exchanger <NUM> but flowing through the same can be provided to the siphon or trap <NUM> from the output pipe <NUM> through the first connecting pipe <NUM> and through the valve <NUM>. So, heated water as well as unheated water can be provided to the siphon or trap <NUM> without any water consumption at a water consumer <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a calibration of the gas burner <NUM> of the water heater <NUM> of <FIG> and <FIG>, the water heater <NUM> is operated as follows: The gas burner <NUM> is operated at a defined calibration burner load for a defined calibration time interval and the water heated by the heat exchanger <NUM> during the calibration is provided by the valve <NUM> to the siphon or trap <NUM>. In this situation the ports 25a, 25c of the valve <NUM> are opened and the port 25b of the valve <NUM> is closed. During the calibration, the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>, namely in such a way that the heated water flows from the first section 19a of the output pipe <NUM> through the valve <NUM> and through the first connecting pipe <NUM> to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a filling the siphon or trap <NUM> directly after installation of the water heater <NUM> of <FIG> and <FIG>, the water heater <NUM> is operated as follows: Unheated water or heated water is provided by the valve <NUM> to the siphon or trap <NUM>. Preferably, the unheated water or the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>. To provide heated water to the siphon or trap <NUM>, the gas burner <NUM> is combusting gas <NUM> at a defined burner load. To provide unheated water to the siphon or trap <NUM>, the gas burner <NUM> is not combusting gas <NUM>. The heated water or the unheated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>, namely in such a way that the water flows from the first section 19a of the output pipe <NUM> through the valve <NUM> and through the first connecting pipe <NUM> to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a cleaning the siphon or trap <NUM> the water heater <NUM> of <FIG> and <FIG> is operated as follows: Unheated water or heated water is provided by the valve <NUM> to the siphon or trap <NUM>. Unheated water or heated water is provided by the valve <NUM> to the siphon or trap <NUM>. Preferably, the unheated water or the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>. To provide heated water to the siphon or trap <NUM>, the gas burner <NUM> is combusting gas <NUM> at a defined burner load. To provide unheated water to the siphon or trap <NUM>, the gas burner <NUM> is not combusting gas <NUM>. The heated water or the unheated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>, namely in such a way that the water flows from the first section 19a of the output pipe <NUM> through the valve <NUM> and through the first connecting pipe <NUM> to the siphon or trap <NUM>.

For the descaling of the heat exchanger <NUM> of the water heater <NUM>, during the first time interval and during the second time interval the water is provided from the output pipe <NUM> to the siphon or trap <NUM> through the valve <NUM>, namely in such a way that the water flows from the first section 19a of the output pipe <NUM> through the valve <NUM> and through the first connecting pipe <NUM> to the siphon or trap <NUM>.

If in <FIG> and <FIG> water flows from output pipe <NUM> to the siphon or trap <NUM>, the ports 25a, 25c of the valve <NUM> are opened and the port 25b of the valve <NUM> is closed.

<FIG> both shows a water heater <NUM> according to a third embodiment of the present invention.

The water heater <NUM> of <FIG> mandatorily comprises the second connecting pipe <NUM> extending between the input pipe <NUM> and the output pipe <NUM>. The second connecting pipe <NUM> may also be called bypass pipe. In <FIG>, the first connecting pipe <NUM> extends between the second connecting pipe <NUM> and the siphon or trap <NUM>. The water heater of <FIG> further comprises a valve <NUM> connected between the first connecting pipe <NUM> and the second connecting pipe <NUM>. Said valve <NUM> is configured to guide water heated by heat exchanger <NUM> from the output pipe <NUM> to the siphon or trap <NUM>, and to guide water unheated by the heat exchanger <NUM> but flowing through the same from the output pipe <NUM> to the siphon or trap <NUM>. This can be done even if no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>. Said valve <NUM> is also configured to guide unheated water bypassing the heat exchanger <NUM> from the input pipe <NUM> to the siphon or trap <NUM>.

The valve <NUM> of <FIG> is a <NUM>-way-valve. A first port 27a of the <NUM>-way-valve <NUM> is connected to output pipe <NUM> through a first section 20a of the second connecting pipe <NUM>. A second port 27b of the <NUM>-way-valve <NUM> is connected to input pipe <NUM> through a second section 20b of the second connecting pipe <NUM>. A third port 27c of the <NUM>-way-valve <NUM> is connected to the siphon or trap <NUM> through the first connecting pipe <NUM>.

If a heat demand is present at the water heater of <FIG>, namely if heated water is requested by the at least one water consumer <NUM>, the input pipe <NUM> provides water to the heat exchanger <NUM>, said water becomes heated by the heat exchanger <NUM> when flowing through the same using the thermal energy resulting from the combustion of the gas <NUM> by the gas burner <NUM>, and the water heated by the heat exchanger <NUM> is provided to the respective water consumer <NUM>. In this situation the valve <NUM> may be closed or opened.

If the valve <NUM> is closed in this situation, only water heated by the heat exchanger <NUM> is provided to the respective water consumer <NUM>. If the valve <NUM> is opened in this situation, the water heated by the heat exchanger <NUM> becomes mixed with unheated water bypassing the heat exchanger and said mixture is provided to the respective water consumer <NUM>.

If a heat demand is not present at the water heater of <FIG>, namely if heated water is not requested by the at least one water consumer <NUM>, the gas burner <NUM> may be active and may combust gas <NUM> or may inactive and may not combust gas <NUM>.

If a heat demand is not present and if the gas burner <NUM> of the water heater of <FIG> is combusting gas <NUM>, water heated by the heat exchanger <NUM> can be provided to the siphon or trap <NUM> from the output pipe <NUM> through the first section 20a of first connecting pipe <NUM>, through the <NUM>-way valve <NUM> and through the second connecting pipe <NUM>.

If a heat demand is not present and if the gas burner <NUM> of the water heater of <FIG> is not combusting gas <NUM>, water not being heated by the heat exchanger <NUM> but flowing through the same can be provided to the siphon or trap <NUM> from the output pipe <NUM> through the first section 20a of first connecting pipe <NUM>, through the <NUM>-way valve <NUM> and through the second connecting pipe <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a calibration of the gas burner <NUM> of the water heater <NUM> of <FIG> the water heater <NUM> is operated as follows: The gas burner <NUM> is operated at a defined calibration burner load for a defined calibration time interval and the water heated by the heat exchanger <NUM> during the calibration is provided by the valve <NUM> to the siphon or trap <NUM>. During the calibration, the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>, namely in such a way that the heater water flows from the output pipe <NUM> through the first section 20a of the first connecting pipe <NUM>, through the valve <NUM> and through the second connection pipe <NUM> to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a filling the siphon or trap <NUM> directly after installation of the water heater <NUM> of <FIG>, the water heater <NUM> is operated as follows: Unheated water or heated water is provided by the valve <NUM> to the siphon or trap <NUM>. Preferably, the unheated water or the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>. To provide heated water to the siphon or trap <NUM>, the gas burner <NUM> is combusting gas <NUM> at a defined burner load. To provide unheated water to the siphon or trap <NUM>, the gas burner <NUM> is not combusting gas <NUM>. The heated water or the unheated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>, namely in such a way that the water flows from the output pipe <NUM> through the first section 20a of the first connecting pipe <NUM>, through the valve <NUM> and through the second connection pipe <NUM> to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a cleaning the siphon or trap <NUM> the water heater <NUM> of <FIG> is operated as follows: Unheated water or heated water is provided by the valve to the siphon or trap <NUM>. Unheated water or heated water is provided by the valve <NUM> to the siphon or trap <NUM>. Preferably, the unheated water or the heated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>. To provide heated water to the siphon or trap <NUM>, the gas burner <NUM> is combusting gas <NUM> at a defined burner load. To provide unheated water to the siphon or trap <NUM>, the gas burner <NUM> is not combusting gas <NUM>. The heated water or the unheated water is provided by the valve <NUM> to the siphon or trap <NUM> from the output pipe <NUM>, namely in such a way that the water flows from the output pipe <NUM> through the first section 20a of the first connecting pipe <NUM>, through the valve <NUM> and through the second connection pipe <NUM> to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not requested by the at least one water consumer <NUM>, for a descaling of the heat exchanger <NUM> the water heater <NUM> of <FIG> is operated as follows. The following steps i) and ii) are alternately executed. Step i): Combust gas with the gas burner <NUM> at a defined burner load for a defined first time interval and provide the heated water to the siphon or trap <NUM>. Step ii): Stop combustion of gas within the gas burner <NUM> for a defined second time interval and provide the unheated water to the siphon or trap <NUM>.

If no heat demand is present, namely if heated water is not re-quested by the at least one water consumer <NUM>, for a descaling of the heat exchanger <NUM> the water heater <NUM> of <FIG> is alternatively operated as follows. The following steps i) and ii) are alternately executed. Step i): Combust gas with the gas burner <NUM> at a defined first burner load for a defined first time interval and provide the heated water to the siphon or trap <NUM>. Step ii) combust gas with the gas burner <NUM> at a defined second burner load for a defined second time interval and provide the heated water to the siphon or trap <NUM>, wherein the first burner load is relatively low compared to the second burner load. The first burner load may be a minimum burner load and the second burner load may be a maximum burner load.

For the descaling of the heat exchanger <NUM> of the water heater <NUM> of <FIG>, during the first time interval and during the second time interval the water is provided from the output pipe <NUM> to the siphon or trap <NUM> through the valve <NUM>, namely in such a way that the water flows from the output pipe <NUM> through the first section 20a of the first connecting pipe <NUM>, through the valve <NUM> and through the second connection pipe <NUM> to the siphon or trap <NUM>.

Claim 1:
Water heater (<NUM>) comprising:
a gas burner (<NUM>) being configured to combust gas if a heat demand is present, namely if heated water is requested by at least one water consumer (<NUM>),
a heat exchanger (<NUM>) being configured to heat water using the thermal energy provided with the combustion of the gas, wherein the heat exchanger (<NUM>) is a condensing heat exchanger,
an input pipe (<NUM>) being configured to provide water to be heated to the heat exchanger (<NUM>),
an output pipe (<NUM>) being configured to provide water heated by the heat exchanger (<NUM>) to the at least one water consumer (<NUM>),
a siphon or trap (<NUM>) being configured to collect condensate resulting at the condensing heat exchanger (<NUM>) during operation of the water heater (<NUM>),
a first connection pipe (<NUM>) and a valve (<NUM>, <NUM>, <NUM>) acting together with the first connection pipe (<NUM>), both the first connection pipe (<NUM>) and the valve (<NUM>, <NUM>, <NUM>) being configured to
guide water heated by heat exchanger (<NUM>) from the output pipe (<NUM>) to the siphon or trap (<NUM>), and/or
guide water not heated by the heat exchanger (<NUM>) from the output pipe (<NUM>) to the siphon or trap (<NUM>),
characterized by
a second connecting pipe (<NUM>) extending between the input pipe (<NUM>) and the output pipe (<NUM>),
wherein in a first alternative a separate valve (<NUM>) acts together with the second connection pipe (<NUM>) being configured to guide water from input pipe (<NUM>) to the output pipe (<NUM>), or
wherein in a second alternative the first connecting pipe (<NUM>) extends between the second connecting pipe (<NUM>) and the siphon or trap (<NUM>), the valve (<NUM>) acting together with the first connection pipe (<NUM>) is provided by a <NUM>-way-valve, is connected between the first connecting pipe (<NUM>) and the second connecting pipe (<NUM>) and acts also together with the second connection pipe (<NUM>), a first port (27a) of the <NUM>-way-valve is connected to the output pipe (<NUM>) through a first section (20a) of the second connecting pipe (<NUM>), a second port (27b) of the <NUM>-way-valve is connected to the input pipe (<NUM>) through a second section (10b) of the second connecting pipe (<NUM>), and a third port (27c) of the <NUM>-way-valve is connected to the siphon or trap (<NUM>) through the first connecting pipe (<NUM>).