Re: Heating won't come on all the time.

Most of the time, when my central heating timer comes on, it does not

> set the heating on. I have to play around with the timer. Often I can
> get it to work by turning the water heating on too but it is very > erratic.

Presumably the water side is calling for heat when you can get the heating to work with the water on as well.

Our thermostat has never affected the heating so it can't be that ...

Why? Together with the above it indicates the room thermostat has a fault to me. Either in it or in the wiring. Check the wiring if that's OK, I suggest suggest replacing it with a programmable thermostat.

In message , newtonbase wrote

Maybe three port valve sticking in the hot water position? The valves have a lever on the side that shows the position - it can be manually moved to help diagnose the fault.

well if the house is warm enough already, why would it?

I haven't had to call for any CH for the last 4 weeks...timer still comes on of course..

I have to play around with the timer. Often I can

??? what on earth does that mean? Thermostats are there to 'affect the heating'. If they aren't affecting the heating they at least are faulty.

If the thermostat is up full and the timer is on, then its probably a buggered motorised valve.

Have you checked the water pressure and topped up if necessary? There's usually a green area on the gauge (probably around 1 bar) that the needle should be in when cold. The pressure will rise when the water gets warm, and getting the hot water working could be nudging it into the OK range.

What kind of "playing" are you doing with the timer? Perhaps you're jiggling a loose wire behind it. Does "percussive maintenance" start/ stop it? As others have said, you need to work through the circuit with a meter, but assuming it keeps going once started, I suspect the problem is within the boiler, with the ineffective (permanently on) thermostat a separate issue.

Does power cycling at the mains connection start it? This could imply something that needs a kick, like a dodgy relay on the circuit board or sticking motorised valve as others have suggested.

I share your distrust of heating engineers. A chap who was prepared to spend hours fixing something when I first met him years ago now tends to recommend a new boiler at every opportunity. OTOH perhaps he knows they're no longer built to last.

Chris