Pressurised water noise when TRV opens


My apartment has heat supplied by district heating scheme and has Danfoss VMTD-F-B substation (so I don't have a gas boiler in my place).

I have an issue with a noise that sounds like a pressurised water entering the radiator when tado opens the TRV. It only happens when system was idle for a while and this is the only TRV opening.

Did anyone have similar experience?

I have spoken to Danfoss and they said there's no need for a bypass in such setup and TRVs can be safely fitted to all radiators in the flat.

What I suspect is happening - when Tado stops calling for heat there is a delay before the tado TRVs on the radiators are being shut. There is a motorised valve in the substation that is actually controlled by the thermostat (tado). I think, that it takes time to shut it and the radiator TRVs shut before this one does, which results in a pressure building in the system between the motorised valve in the substation and the TRVs on the radiators. When the room calls for heat, TRV opens first and releases the pressurised water.

I didn't experience any other issues apart from the noise. Did anyone find a solution to that?

I can personally think of 2 options:

1) Tado always keeping at least one TRV partly open when system is off - what I mean is that once no room calls for heat and Tado thermostat stops calling the substation for heat, at least one Tado TRV is partly open when the system is completely off. This means, that before the motorised valve in the distric heating substation closes completely, there will be a minimum flow maintained to avoid building a pressure. It would be a sort of "soft" bypass valve. It would require Tado to work such logic into the system.

2) A hardware TRV body that has a pressure sensor - I am not sure if something like that exists - if it does please let me know - essentially such valve would work as a TRV under normal circumstances, but if the pressure in the system would go above set value, the valve would give in and "override" the TRV's sensing head current state.

Any suggestions are much appreciated.


  • do you have variable speed pumps? if not, this is typical to happen as the water flow is constant per fixed speed pump and therefore water going through the only open TRV will make a lot of noise since the pressure is too large.

    based on the above, your point number 2 is on the right track. However, t the solution is not the TRV, but on your water pumps that need to be variable speed. they could already have that setting, but could be set to a fixed speed.