Central Heating Advice

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Mon 10 Mar 2014 11:26
Central Heating Advice - Ben 10

CH is on timer for HW and CH. Both came on this morning. CH for 2 hours timed. HW on for once.

Noticed about 11.00 that the HW was on the CH off as indicated, yet there was heat coming from the radiators. There should be no heat from the rads. Has a valve gone at the boiler or is it something else?

Any responses much appreciated.

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Mon 10 Mar 2014 11:38
Central Heating Advice - gordonbennet

I'm no heating expert, but from my experience as this was recent problem here :-

Presumably the CH pump is still running, switch off at the timer and give it a few minutes to shut down, if it doesn't shut down turn the boiler off at the mains.

Do you have thermostatic valves on every rad?, if so and they all shut then the pump can become stuck on, one rad should have no thermostat to allow circulation if the others all shut down together (unless your system is designed from stratch to suit but way above my pay grade), turning one of the bathroom rads up to full heat should alleviate this if indeed it's anything to do with it, but once the pump switch is stuck 'on' it might need help to switch off.

Shutting the power off at the boiler and allowing things to cool for a while should allow a restart, and i would do that anyway.

Since intervening and shutting all down and restarting, ours has been fine.

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Mon 10 Mar 2014 11:42
Central Heating Advice - FP

From past experience, I would first of all suspect motorised valves. It's possible the pump has continued to run, as HW is being called for, but the CH circuit, instead of being closed by the motorised valve, has been left open by the valve sticking.

If you are DIY-minded, you can disconnect the electricity to the motor of a valve, take off the motor unit and see how freely the valve spindle moves, using an adjustable spanner or (with care) pliers. Sometimes a twiddle of the spindle will free the valve enough for it to function, though there's always the chance it will stick again.

You mention a valve "at the boiler", but these are often situated elsewhere - both mine are in the airing cupboard, near the hot water cylinder.

The other culprit could be the programmer itself.

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Mon 10 Mar 2014 17:34
Central Heating Advice - Ben 10

I too think it may be the motorised valve. Mine is in a cupboard that houses the boiler and pump. I'll have a go at seeing if I can free it first. Otherwise I'll have to change. My expeience from the past is that these valves go wrong pretty regular. Is there not a more reliable unit available?

Edited by Ben 10 on 10/03/2014 at 17:39

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Mon 10 Mar 2014 18:18
Central Heating Advice - FP

"...these valves go wrong pretty regular. Is there not a more reliable unit available?"

It does seem a very common problem. My heating engineer (who replaced one of mine last autumn) said it was very hit-and-miss and he had known examples that lasted for many years, while others fail after a short life.

It's worth pointing out that, for the valves to rotate freely, a suitable additive must be used in the circulating water, to prevent corrosion and thus keep the water free from crud. If a system is losing pressure or has leaks and is topped up frequently, the additive gets diluted.

Edited by FP on 10/03/2014 at 18:20

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