Why doesn't my heating work?

[DamnSkippy]

I have a Worcester Greenstar boiler with a Honeywell CM907 digital thermostat. We have had the heating turned off at the thermostat over the Summer - turned it on about 3-weeks ago to find that it doesn't work. The little flame symbol appears in the display on the stat but the boiler doesn't fire up.

A couple of times I have left the heating on manual and around 2-3 hours later the boiler has actually fired up and heated the radiators but I don't know why and I'm not able to make it come on when I want it to.

The boiler was serviced around 6-months ago, so I'm thinking this is more likely to be a problem with the stat?

Any suggestions would be welcome - it was bloody freezing this morning!

Presumably it isn't set to heat water only? What temperature is the thermostat set to?

It's a combi boiler so the stat just controls the heating. The heating/water/pressure settings on the boiler are as they should be.

The temp is set to 19 degrees. I've tried turning it up to 22/23 but the boiler still doesn't fire.

The hot water has been working fine all the time the heating has been off.

Do you have a white box with a button and light by the boiler we have a worchester boiler and Honeywell remote thermostat. Sometimes the reset button on this box sorts everything out

gingercat02 - is your thermostat wireless? I don't have a box by the boiler but my thermostat is wired.

Does the stat need new batteries?

Oh sorry it's wired. I'm no help then!

Ours is wireless too sorry

The CM907 is wired, not wireless. It does have batteries to operate the timer and display but they last several years and I'd expect the display to fade before the timer stopped working.

You haven't got Weather Compensation, have you?

Hi Piglet John

No, I haven't got Weather Compensation.

The boiler has an analogue timer on it, which was over-ridden when we installed the digital thermostat. If I disable the digital thermostat, then I presume the timer on the boiler will work again? But there won't be a thermostat - can I control the room temp using the radiator dial on the boiler?

The thermostat quite a simple instrument, it's unusual for it to fail.

You could try changing the batteries, though I doubt that's the problem, and check all the settings.

Is the boiler timer definitely set to 24-hour on?

A person competent with electrical work could easily bridge the two wires that go into the thermostat. If the thermostat is at fault that would put the CH on constantly, so you'd know what needed changing. Adjusting the boiler thermostat will reduce the temperature of the radiators, but unless you have TRVs will be rather inaccurate. Anyway, it will waste gas by running when not needed. You could use the boiler timer (if still operational) to set the times.

As it's now a last-year's-model, a CM907 is now available at discount. It's a very good programmable thermostat, and less likely to go wrong than a wireless or Smart one.

Thanks Piglet John

I do have TRVs. I really just want to confirm that the boiler is working correctly before replacing the thermostat. I suspect that my current problems are caused by either the thermostat or the wiring between the stat and the boiler.

I have been thinking of getting a Hive system and I think that this would solve these problems as I believe that the receiver is wired near the boiler, rather than in place of the old wired thermostat?

wires very rarely go wrong unless someone hammers a nail into them. If you go for a wireless or smart system the receiver would usually go next to the boiler. However IMO you are more likely to find it troublesome.

Hi @PigletJohn can I ask you a question? I have one radiator that doesn't work. I've tried it on different settings (the knob at the base of the radiator) and it still won't come on. I've tried twisting the knob on the other end. Do I need to get someone out to see it? Thanks.

turn off ALL the others. Does it now warm up? Post a pic of both the valves at the ends of the rad. How old is your heating system?

Hi, the heating system is from 1985 so over 35 years old! I haven't turned the others off yet but I'll try that tomorrow. Thanks for getting back to me so soon. Here are the pics.

OP, do you maybe have to reset the thermostat because it was switched off over the summer?

Just to check the really obvious thing, have you whacked the thermostat up to max? 19deg might not have been enough to trigger it before.

I had the same problem turned out someone was on my frequency for my thermostat. Change the frequency and all was fine. Hope you get it sorted soon, I've just put my heating on

@bobbinsand I think you should start your own thread because you have a different problem.

Some developments with the boiler issues this evening! Took the batteries out of the stat all day today - we were hoping to reset to factory programme. Put the batteries back in, set it to manual and the boiler fired up! Hooray! Then later in the evening my husband noticed there was no hot water. Checked the boiler and the pressure is down to 0. Tried turning the valve and the boiler makes a lot of noise but the pressure won't go up. So sadly it does seem to be a problem with the boiler after all and we will need to get a man out. Thanks for all your help and suggestions though!

Hope you get it sorted soon.It worked intermittently and then stopped completely. Was the thermostat battery running out. Ours might have lost pressure too. Shot in the dark but maybe put new batteries in for a last ditch attempt?!?

Just read your update properly, perhaps past the point of thermostat batteries

"turning the valve and the boiler makes a lot of noise but the pressure won't go up." then you have a leak. Quite likely the pressure valve that vents to the outside through the wall behind the boiler is letting it squirt out. Have a look at the outside wall when it is light. This valve should only open when the pressure is above the upper limit, but once opened, they don't always shut correctly. Some other type of leak might be more serious so look for any signs or smells of damp.

I have had a similar problem. My heating came on for no reason at all in hot weather. It turns out the thermostat needed new batteries (I've already replaced them this year). Apparently RF stats go into emergency mode and start the heating without demand.