is not from the mains supply, but is condensation caused by the efficient operation of the water heater. On cool days it is common to see clouds of water vapour coming from the flue of the Rheem Stellar when in operation. This may be mistaken for smoke. The Stellar's high efficiency this is why the flue gases and vapour are visible. This is not a fault. Condense also forms in the flue and is discharged from a small pipe on the left side of the cylinder at the base. This is not a water leak. During heavy use or in cold atmospheric conditions large amounts of condense can form in the flue. This condense will run down the flue and can be seen on the top of the water heater.  This is not a water leak. Also during operation hissing can be heard as water condense drips onto the burner. Again, this is normal operation and not a water leak. Is the electricity switched on? Check the switch marked "water heater" at the switchboard and the isolating switch, if one is installed, near the water heater. Note: Where the water heater is connected to an "OFF-PEAK" or controlled electrical tariff, the supply may not be available at certain times of the day. For Twin element non-simultaneous models, power must be available to top circuit at all times for this water heater to operate as designed. Do you have the correct size water heater for your requirements? The sizing guide in