Hot water on / Rads off = Warm Rads

SimonEdwards

Anyone here help with some advice, please...

My heating / water system comprises of an oil boiler that has two pumps, one pump for the hot water, one pump for the central heating.

When I turn my hot water on the hot water pump starts and water goes from the boiler to the hot water cylinder upstairs in the bathroom. But, although the central heating pump is off some of my radiators warm up. My limited knowledge of plumbing is that the hot water rises so this is what is heating my rads up. Other than this it all works perfectly.

My question is what should I do to stop this happening, I don't want hot rads in the summer when I have the hot water on.

Many thanks! Simon.

Grenage

This sounds like a three-way valve that isn't closing properly. I had this with my boiler, and the motorised valve head needed replacing.


Assuming you have such a valve, there will likely be a manual lever on it that allows you to push it over to the domestic hot water position. it could be sitting in the middle, or just slightly off.

Wassa123

What radiators? My bathroom radiators seem to be plumbed into the hot water. I just turn them off in Summer.


However, this can also occur due to a failed valve which separates the hot water and heating systems. I've seen it mentioned several times on here before but that's as much as I know. (Edit: see above)

SimonEdwards

Thanks, just to clarify I don't seem to have a valve on the system - instead two pumps...

Grenage

But probably only one boiler, so there must be something dictating where the water goes.


I will openly admit that I am not a heating engineer, just a DIYer.

Alex1983

Maybe a non return valve on the heating circuit jammed up allowing the hot water return back around the heating system.

Rodders53

Hot water rises as it is slightly lighter than cold water which is denser and sinks, this can allow water to circulate. This is how 'gravity fed' hot water tanks used to operate. Pumps will not act like valves and may well allow some water to pass by due to the other pump running and the pressure differences that causes in the pipework.

The simplest solution is to turn off the affected radiators in the Summertime using either the Thermostatic Valve or handwheel.

Very occasionally bathroom towel rails or radiators are deliberately connected into the hot water tank feed to warm the room / dry towels all year round. This would be obvious from the speed of heating up cf gravity or passing by circulation of heated water.

Sometimes even motorised valve that should shut off a water supply route do not close completely allowing water to pass by. So although fitting one is an alternative solution it would need to electrically interlock with the CH pump.