Upstairs radiators coming on when only hot water should be running

[ZeroTools]

Hi all,

I have noticed these last few days (having only just switched off my heating), that when the hot water comes on, the radiators upstairs are also coming on (downstairs remain cold). I suspect this is an issue with the 3-way valve or some related item but just wanted to see if there was any advice on checks or fixes I could apply myself before calling in an engineer. I know the simplest solution in the short term would be to shut the valves on the upstairs rads, but unfortunately they're almost all knackered and leak when closed or are seized fully open.

I've checked the actuator head (which is a BGMVSP-23) and when switching between hot water only and heating+water, the little switch on the side is moving between the W and M positions, and it is set at the correct position when the water only is on. However all 3 pipes from the valve are hot when only running the hot water. We recently had some rads and valves replaced downstairs and had a few weeks of issues with airlocks and balancing the system afterwards. Not sure if this could be related or not (though I thought we had resolved all those now).

If I understand correctly then the actuator can be removed and the valve tested independently (though I've no idea how to do this). I'm happy doing some basic checks but if it's likely a drain down and replacement of anything plumbing related is required I will just get a professional in. Any advice welcome.

 

[oilhead]

The 3 port valve could be passing a little but not enough to reach downstairs, or it could be thermo syphoning from a shared return. A professional should be able to determine which.

 

[stem]

It could be incorrect piping causing 'reverse circulation'. This occurs when the hot water return isn't the last connection into the return pipework to the boiler and causes water to circulate in a reverse direction through some of the radiators when the hot water is on. However, this fault wouldn't just appear, it would have been present since the pipework was installed or changed, and in this case, the heating flow pipe from the motorised valve wouldn't be 'hot' other than immediately adjacent to the valve where it would be heated by conduction rather than water flow.

 

[ZeroTools]

Thanks for the advice. Following a recommendation from another forum, I tried switching the heating back on and giving the valve some light 'persuasion' with the aid of a hammer. Fingers crossed it seems to have sorted the issue, at least for now.