I live in a condominium unit and have a thermostatic control valve in my shower. I have just been advised that it is faulty (asymptomatic to me because I don't have any problem with water temperature which has always been set at the optimal 38 degree C ). The alleged faulty valve is causing temperature fluctuations in showers on floors above and below me. How can I verify that my valve is faulty? Can I install a check valve ( what type ?) in my hot or cold water supply lines to the shower to prevent future potential crossover problems ( will happen over time arising from a faulty in the valve due to wear and tear ) affecting showers in other unit(s) on the same supply line due to a faulty valve in my shower?


2 Answers 2


This answer is only relevant if your building has a central hot water system.

The faulty valve (anti-scald, mixing, or tempering valve) may let cold water backflow into the central hot water system giving lukewarm showers to your neighbors - except when you are showering. If so, a non-return valve (tap, faucet) on the hot water inlet would prevent this. But your system might not be like this.

I have seen this happen.

  • My building has a central hot water system. I have a manually operated " shut off" to my shower control valve on both the hot and cold water supply lines connected to the main water supply risers in the building. Do I just have to install a non-return valve on only the hot water inlet? And on which side ( the supply line side or the shower side) of the manual shut off ? I presume I will have to install one non-return for each of my two showers right ?
    – Chan
    Jul 19, 2021 at 3:12
  • 1
    Mention the region of the world where you are, then a local can give a code-specific answer. (Different regulations everywhere) Jul 19, 2021 at 7:58
  • In the building I saw, they replaced about 10 of these valves. One issue ignored was whether each apartment should have had a non-return valve (required here in Australia), or just the whole apartment block. Some people were getting big water bills when they weren't home. Jul 29, 2021 at 23:07

Multi unit housing sometimes have shutoffs built into the shower valves so a cartridge replacement can be done without shutting water to the entire building. You can remove the plate and see if there's a way to shut of the supply to the valve. If so shutting those supply valves for a day or two should help determine if it's your mixer or not.

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