A gas valve unit for controlling gas flow in a heating apparatus, the gas valve unit comprising: a coil configured to generate a magnetic field in response to an input signal; a valve member movable in response to the magnetic field to cause displacement of at least one valve element (106, 114) relative to a valve opening and relative to at least one valve seat (103, 103A, 103B), to adjust a gas flow rate through the valve opening by varying an extent of opening area in the opening relative to the at least one valve seat; a sensor configured to provide an output indicative of a pressure at an outlet of the gas valve unit; a setting device that provides an input for selection of at least one opening flow rate profile that is a function describing desired outlet pressure over time during a valve opening phase for establishing combustion, where a selected opening flow rate profile is suitable for being used in controlling gas flow for initially establishing combustion in the heating apparatus; a main diaphragm chamber; a main diaphragm in the main diaphragm chamber and configured to controllably displace the valve member and valve element relative to the valve opening to adjust the gas flow rate in response to changes in pressure in the main diaphragm chamber; a servo-regulator diaphragm configured to regulate fluid flow to the main diaphragm chamber; a stepper motor in which the coil is configured to generate the magnetic field, the stepper motor configured to move in a stepwise manner to bias the servo-regulator diaphragm for regulating fluid flow to the main diaphragm chamber to cause the displacement of the main diaphragm, the valve member and the valve element to control the gas flow rate through the gas valve unit; a valve controller configured to control, based at least in part on the output from the sensor that is indicative of pressure at the outlet, the input signal to the coil of the stepper motor for controlling movement of the valve member and the at least one valve element relative to the valve opening for controlling the gas flow rate through the outlet, the valve controller being selectively configurable to provide a desired outlet pressure over time in accordance with the opening flow rate profile selected by the setting device, wherein the valve controller is configured to average a difference between a sensed outlet pressure and a stored outlet pressure value corresponding to the selected opening flow rate profile over multiple successive gas ignition cycles, and to adjust the input signal to the coil of the stepper motor to approximate the selected opening flow rate profile according to said averaged difference. a coil configured to generate a magnetic field in response to an input signal; a valve member movable in response to the magnetic field to cause displacement of at least one valve element (106, 114) relative to a valve opening and relative to at least one valve seat (103, 103A, 103B), to adjust a gas flow rate through the valve opening by varying an extent of opening area in the opening relative to the at least one valve seat; a sensor configured to provide an output indicative of a pressure at an outlet of the gas valve unit; a setting device that provides an input for selection of at least one opening flow rate profile that is a function describing desired outlet pressure over time during a valve opening phase for establishing combustion, where a selected opening flow rate profile is suitable for being used in controlling gas flow for initially establishing combustion in the heating apparatus; a main diaphragm chamber; a main diaphragm in the main diaphragm chamber and configured to controllably displace the valve member and valve element relative to the valve opening to adjust the gas flow rate in response to changes in pressure in the main diaphragm chamber; a servo-regulator diaphragm configured to regulate fluid flow to the main diaphragm chamber; a stepper motor in which the coil is configured to generate the magnetic field, the stepper motor configured to move in a stepwise manner to bias the servo-regulator diaphragm for regulating fluid flow to the main diaphragm chamber to cause the displacement of the main diaphragm, the valve member and the valve element to control the gas flow rate through the gas valve unit; a valve controller configured to control, based at least in part on the output from the sensor that is indicative of pressure at the outlet, the input signal to the coil of the stepper motor for controlling movement of the valve member and the at least one valve element relative to the valve opening for controlling the gas flow rate through the outlet, the valve controller being selectively configurable to provide a desired outlet pressure over time in accordance with the opening flow rate profile selected by the setting device, wherein the valve controller is configured to average a difference between a sensed outlet pressure and a stored outlet pressure value corresponding to the selected opening flow rate profile over multiple successive gas ignition cycles, and to adjust the input signal to the coil of the stepper motor to approximate the selected opening flow rate profile according to said averaged difference.