I have just had a new electric water heater installed, the previous one was leaking. When the temperature of the water thermostat approaches cut-off the safety relief valve drips and the water pressure approaches 9 bar as indicated on the gauge fitted on the pressure reducing valve (PRV). Pressure then drops down to 4 bar and the dripping from the safety relief valve stops.
My plumber advises that the PRV could be faulty, however I note from the users guide that " After five to twenty minutes , according to the capacity of the appliance, water should start dripping from the drain outlet. This is normal and results from expansion of the water."
I'm somewhat confused and would appreciate your advise on the functionality
PRV and dripping outlet.

Many thanks

Hi Thebrook:

Is this PRV valve new with this installation.. If so, it probably has an internal check valve that is creating what is referred to as a CLOSED SYSTEM.

Here, water expands as it is heated and if the system is a closed system there is no place for the water to expand EXCEPT out the relief valve. A dripping relief valve is not acceptable, and replacing the valve will not alleviate this issue!

In this case, you will need to have a water heater expansion tank installed in the cold water inlet to the heater (after the PRV valve). See the pictures below... ;)

If you read the instructions supplied with the water heater it should go into pretty good detail about THERMAL EXPANSION.

Let me know what you think here... MARK