Drayton LP522 not firing central heating

[Leo21]

They usually were, just wired into Randal 103,s. So it went of on the cylinder stat. But no option on the clock .

 

[BowerHinton]

Many thanks for all the advice and especially to learnplum who suggested where to measure. With heating on and room stat at max the white wire is about 240 volts and the orange wire about 38 volts. There are two sets of gray wires, one set measures about 240 volts as long as power is on.

So it looks like I need to get a plumber to replace the valve, right?

 

[learnplum]

Yipppppeeeeeee, I may of gave a little bit of advice, instead of asking for it.:tounge_smile:
Ok not sure why you have two greys, at the join, unless you have a new coloured coded cable, from the clock to the join.
(new colours, brown/black/grey).
But if you identify, the grey of the valve, and this has 230volts on it, and at the same time, the white of the valve, has 230volts on it, then you should have 230volts, on the orange of the valve.
The valve uses the grey to signal to the orange, to fire the boiler up.
Power on the white only, holds it in mid-position.
So central heating and hot water in that position.
By gettin 230v on white, you have proved the clock and stat are ok.:tounge_smile:

 

[BowerHinton]

Well oddly enough the CH started working all of a sudden last night. My wife thinks I've fixed it and I don't like to tell her I only measured a few things! I guess there is something sticky in the valve causing intermittent failures but at least I know what to replace to fix it permanently.