Hot Water Staying Hot Even Though Turned Off

A customer rang me to have a look at his hot water today as he was getting plenty of hot water even though it had not been set to come on for almost a week. Quite often I go to have a look at this fault to find that the immersion heater has been turned on by the wife or kids! When I looked in the airing cupboard the immersion heater was wired into a plug and clearly unplugged.

Looking at the timer the central heating was set to be on through the day and the hot water was off.  I turned up the room thermostat to bring the pump and boiler on. I then waited in the airing cupboard feeling the pipes to find out where the heat was going. The heat appeared between the pump and motorised valve first of all and could be felt going to the radiator circuit. The radiator circuit being port A of the motorised valve. The pipework between the valve and the motorised valve was very short making it difficult to gauge the temperature of the hot water travelling within the pipe due to the transfer of heat back from the cylinder. I felt the pipe on the cylinder return, which is the lower connection and could feel it slowly starting to get warm.

I decided that it was almost definitely the motorised valve at fault and decide to replace it. When the valve had been removed I could see that when the valve was in the central heating position port B for the hot water was not being closed off fully. Had the valve been open wider I'm sure the customer would have been complaining that their hot water was excessively hot because it would have been heating the whole time the heating came on.

I replaced the motorised valve and retested the system to make sure that the valve was moving as it should and that their was no air in the system and all the radiators got hot. Once everything was up and running I left the heating and hot water set on the timer.

Disclaimer: The works described in this blog are a record of work undertaken and should not be taken as guaranteed to solve your problem. Work should only be carried out by persons qualified and competent to do so.