DIY Doctor

Rads Cooler When Water is on in Single Pipe System

Postby mrmojorisin04 » Tue Nov 20, 2018 12:27 pm


I believe I have a single pipe system and am finding that when both water and heating are set to on, the radiators only get warm: even after a couple of hours. If I switch the water off, then they get nice and hot (although the last couple are not as hot, as expected). The boiler does start and stop quite a bit and the boiler casing feels very hot.

Nearly all the rads all have TRV4 valves on them, so I'm thinking that's probably the issue. If I set the pump to the highest setting then the rads do get fairly hot, but still not as hot as they do when the water is off.

There doesn't seem to be any sludge - the rads can all get hot from top to bottom - so I'm guessing it's a flow problem magnified by the use of TRVs. Is my best option to drain and replace all those valves with manuals? I know a dual pipe system would be better but a full re-pipe isn't really an option at the moment and things do kind of work.

In the meantime would it help if I opened all the lock-shields to improve the flow on the basis that increased flow albeit with heat loss along the way would be better than the hot flow partially missing the rads altogether? The return pipe into the boiler doesn't feel all that hot though.

Or maybe the system just isn't switching across to heating when the water tank is ready? It makes sense to me that the rads would be cooler while the tank is heating, but not for hours. The thermostat on the tank does seem to be working as I can tell the difference if I increase/decrease the temp.

Many thanks for any advice.
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