I have this safety valve that comes with a non-return valve in it:

enter image description here

I'm wondering if the expansion tank should be installed in x1 or x2 point:

enter image description here

Also, should I get a safety valve with max. 8 bar, or max. 6 bar is good enough?

more details:

  • the real pressure in the pipe of cold water intake is 4 bar
  • expansion tank states that the maximum pressure the tank can withstand is 8 bar
  • safety valve stats say that the maximum pressure the valve can withstand is 6 bar

the situation is as follows: I'm trying to connect the heat pump unit to the cold water intake. the heat pump unit has a tank inside and produces hot domestic water & also water for underfloor heating. The issue is that I am not sure if

expansion tank should be installed between safety valve and heat pump unit


safety valve should be installed between expansion tank and heat pump unit
  • What exactly is the situation you are using this for?
    – RMDman
    Feb 14, 2023 at 13:26
  • 1
    As already answered here diy.stackexchange.com/q/266605/18078 it goes as close to the pump intake as possible. Also, the pressures on this diagram make no sense at all.
    – Ecnerwal
    Feb 14, 2023 at 13:54
  • @RMDman the situation is "intake of cold water into the heat pump unit where there is a tank that produces hot water for domestic usage as well as for underfloor heating"
    – servant0
    Feb 14, 2023 at 16:10
  • @Ecnerwal I believe this is a different scenario from the previous question that was about loop for underfloor heating. this one is direct intake of cold water for production of domestic hot water. goes as close to the pump intake as possible - but which one? safety valve or expansion tank goes as close as possible? to explain those pressures... 4 bar is real pressure in the pipe. expansion tank maximum pressure is 8 bar. and the safety valve maximum pressure is 6 bar
    – servant0
    Feb 14, 2023 at 16:18

1 Answer 1


expansion tank should be installed between safety valve and heat pump unit

That is your answer.

This answer assumes that the non-return valve is to stop water flom flowing back from your heater into the cold water supply (correct me if I have assumed the purpose to be wrong here, but in a domestic water supply situation i.e. not a closed heating loop, that is the point of the check valve).

The expansion tank should go between the check valve and the heater input. This allows the natural expansion of heated water to dissipate extra pressure into the tank instead of pushing back on the check valve and potentially damaging the valve or piping.

  • Check valve, non-return valve, backflow prevention valve, are all interchangeable terms for the same thing. They all prevent fluid from flowing in both directions in a pipe. But yes, the expansion tank needs to go wherever expansion could cause damage - that is, after check valve, but before heater. The assumption is that pressure expansion in the other direction is safer because the pipe runs are longer. It also saves your boiler by giving pressure somewhere to go instead of blowing the TPR valve, which are not designed for frequent use.
    – Chris O
    Feb 16, 2023 at 15:55

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