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  • FIRST POST
    • big mortgage
    • By big mortgage 12th Jan 18, 5:51 PM
    • 177Posts
    • 22Thanks
    big mortgage
    Shower thermostatic cartridge: cold leaking across to hot
    • #1
    • 12th Jan 18, 5:51 PM
    Shower thermostatic cartridge: cold leaking across to hot 12th Jan 18 at 5:51 PM
    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...?
Page 1
    • Norman Castle
    • By Norman Castle 13th Jan 18, 1:55 PM
    • 6,512 Posts
    • 5,300 Thanks
    Norman Castle
    • #2
    • 13th Jan 18, 1:55 PM
    • #2
    • 13th Jan 18, 1:55 PM
    Have you got isolation valves for the shower? If so turn them off and see if the problem remains.
    Don't harass a hippie. You'll get bad karma.
    • big mortgage
    • By big mortgage 13th Jan 18, 2:28 PM
    • 177 Posts
    • 22 Thanks
    big mortgage
    • #3
    • 13th Jan 18, 2:28 PM
    • #3
    • 13th Jan 18, 2:28 PM
    Not for the shower specifically. Though the hot water was turned off and water came from the hot tap.
    • EachPenny
    • By EachPenny 14th Jan 18, 12:07 PM
    • 3,982 Posts
    • 8,119 Thanks
    EachPenny
    • #4
    • 14th Jan 18, 12:07 PM
    • #4
    • 14th Jan 18, 12:07 PM
    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!
    Originally posted by big mortgage
    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.
    "In the future, everyone will be rich for 15 minutes"
    • big mortgage
    • By big mortgage 14th Jan 18, 5:01 PM
    • 177 Posts
    • 22 Thanks
    big mortgage
    • #5
    • 14th Jan 18, 5:01 PM
    • #5
    • 14th Jan 18, 5:01 PM
    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
    • By thebullsback 14th Jan 18, 5:26 PM
    • 372 Posts
    • 37 Thanks
    thebullsback
    • #6
    • 14th Jan 18, 5:26 PM
    • #6
    • 14th Jan 18, 5:26 PM
    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.
    Keep in your thoughts the poor Beasts of burden around the World and curse All who do them harm.
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