Radiators only warm when hot water is on.

[wrighty208]

Hi, I have a standard open-vented system with an old back boiler behind a fireplace downstairs feeding 7 radiators. Recently I've noticed whilst the hot water is also on the radiators only seem to get luke warm - when I turn off the hot water they get red hot.

The pipes in and out of the pump and motorised valve always seem hot.

Any ideas?

 

[Slugbabydotcom]

Two ideas

Least likely first

1 An unserviced boiler doesnt create as much heat as it should do if its started to choke up with carbon and/or the gas pressure isnt properly adjusted. Has your boiler been serviced lately?

2 A diverter valve shares the flow of water from your boiler equally between the HW and CH yet the HW part of the circuit goes through a coil and straight back to the boiler [effectively a short circuit]. A system with a lot of resistance through its CH circuit due to an airlock or long runs of CH pipework or sludge [most likely] will be harder work for your pump. To counter this you could try turning your pump up a notch if thats possible otherwise it could be time for a powerflush and/or you may have to accept that this is a fact of life with an older sytem.

 

[Agile]

You should have a lockshield valve on the HW circuit to differentially balance this with the CH.

Close this a little at a time until the CH improves.

If there is none then drain system and fit one!

Tony

 

[bengasman]

In addition to the aforementioned, which is all true: set the programmer so that the hot water starts and finishes before the heating comes on. As it is a backboiler, the f&e tank, pipes and rads are probably full of sludge too which does not help