Shower thermostatic cartridge: cold leaking across to hot

big_mortgage

Hi All,

I replaced the thermostatic cartridge in my shower that was eight years old 1 year ago. This was fed by a conventional back boiler via a twin 3.0 bar pump up until July when the boiler was replaced by a combi. Therefore there is now mains on the cold supply. (the pump was removed.

A few months after having the boiler replaced all the hot water taps in the house run tepid. The engineer who fitter the boiler tells me that the cartridge has failed and leaks cold through to the hot and that is the cause of the tepid water, throughout (hot taps in) the house.


I understand that these have a limit of operation for the pressure differential when operating, but how about when the shower is off? Can they fail this way too? I know I was probably lucky to get eight years out of the first one!

I can see that a seal could have failed, but after one year...?

Norman_Castle

Have you got isolation valves for the shower? If so turn them off and see if the problem remains.

big_mortgage

Not for the shower specifically. Though the hot water was turned off and water came from the hot tap.

EachPenny

big_mortgage wrote: »

I understand that these have a limit of operation for the pressure differential when operating, but how about when the shower is off? Can they fail this way too? I know I was probably lucky to get eight years out of the first one!

It possibly depends on the way the internal mechanism of the valve is configured. If the volume (flow) control is after the mixing point then there might be a path for cold water to flow through the valve into the hot system. That would be a bad bit of design, but these days you cannot rely on things like bathroom fittings to be designed well.

If the hot water for the shower is coming from a combi boiler then you'd expect only a relatively small pressure differential between the hot and cold feeds. If other taps in the house are running tepid because cold water is passing through the shower valve then it implies that there is a more serious pressure-loss through the boiler and hot water pipework than might be expected.

If the more obvious things like isolation valves not being fully on can be ruled out, then it might be possible to add a check valve to the shower's hot feed in order to prevent backflow from the cold feed. This is something you might want to discuss with your plumber.

big_mortgage

Thank you. I believe the flow control is after the mixer. I will check the isolation valves, but don’t think it is them

thebullsback

If you know the make of your shower try telephoning the manufacturers technical help line ( If they have one) and explain your problem.
I have replaced 2 cartridges in my combi fed shower and on both occasions only the shower temperature was affected not the other taps.