DIY Doctor UK DIY Forums

Hi Folks

I have a strange intermittent problem with my gas central heating and wonder if any of you could offer a solution. For some unknown reason the heating goes off two or three times during the day for no apparent reason.

I have replaced the Honeywell room stat situated in a cool hall just in case that was faulty and also replaced the Drayton motorised valve and also the Danfoss timer - all to no avail. Even with the hall stat on 25/30c the heating still goes off even though the true temp in the hall is less than 20c.

On the hot water cylinder is a Honeywell L641A thermostat [u]and only if I turn the temp up to say 70-80c does the heating kick back in. It's as if the whole system seems to want to just heat the cylinder water. I'm wondering if this cylinder stat could be faulty but can't see how this would effect the heating part of the system. The motorised valve shows it is auto switched to 'H' for heating (it moves to 'W' for water when heating the hotwater cylinder.

As usual, it always happens during a cold spell and over a holiday period so it was a cold Christmas for us !!

Hope someone can suggest a remedy.....

Happy New Year to you all. :D

Malcolm

The tank stat should make no difference to the heating side except of course it will turn the boiler on if it calls for heat.

do you have a multimeter? Are you happy to test the heating electrical circuit bearing in mind the risk of live electrics?

If so, with the heating supposedly on but not working and the tank stat turned right down, what voltage is shown at the white wire and the orange wire of the mid position valve?

Is this a newly occurred fault?

Hi Marrtin
Thanks so much for taking the time to respond to my problem - it is greatly appreciated.

I take it from your comment you suspect it may be an electrical wiring problem (?)

I haven't got a 'multimeter' but no doubt have friends that do have.

The problem started with the heating going off for perhaps a day or so and a friend of mine who knows quite a lot about plumbing (but not electrics) said it was a faulty Drayton mid-position valve as when you fiddled with the lever, the boiler fired up, athough at this stage, we were getting very hot water. He replaced the whole valve and I connected the electric side.

Prior to this, on my own instigation, I disconnected and replaced with new the Randal Danfoss timer progammer as the heating had been going off for say 24 hours and then kick in again based on the timing program. It wouldn't kick in when switched to constant hence my perhaps misguided thought of it being down to the timer.

The Drayton valve was the next thing replaced as I mentioned above but again, apart from increasing the temp on the tank stat, the heating would go off.

Finally, as it was not much cost, I replaced the Honeywell room stat but still no solution. I noticed when replacing this stat that the earth wire was not connected to the old stat - just folded back. The new stat has an Earth point but on the wiring diagram does not indicate it has to be connected. Could this be a problem ?

I am going to recheck tightness of wiring connections to the motorised valve, program timer and room stat just in case something is not quite connecting - would this be a wise course to follow to start with.

Marrtin, it is so kind of you and anyone else on the DIY Doctor forum to take the time to help people in trouble. It proves that in this sometimes sad world people do care !

Malcolm

Hi again Marrtin

I've checked and tightened all of the connections as per my last post and all [i]seems[/i] OK.

However, I have noticed that when the Danfoss 'Water Switch' is put in the 'off' position, the motorised valve switches itself off although the indicator is showing at position 'H'

If I switch the Danfoss 'Heating Switch' to off, the valve kicks in and the indicator shows at position 'W'

Unfortunately, I'm a Travel Consultant and very much a novice at this but, it tells me that somehow power or the wiring is wrong and not telling the valve or system to switch to heating only.

Am I right in this assumption or going down the wrong path ?

Malcolm