boiler not firing up

[Newby2]

I have an old glowworm space saver MK2 boiler. It was serviced a month ago and has been working fine until yesterday. It stops firing up, I turned up the thermostat, checked the fuse, checked the timer, but it simply did not fire. The pilot light is there.
I read online that the no.1 reason is lack of electric power. How can I check that?

Any advice is much appreciated.

 

[Newby2]

just an update. When I turned on the hot water, the boiler fired up. It looked like the thermostat is faulty. I have booked a BG engineer but they will come on 23 Dec. Before that, how can I keep the heating on while the thermostat is gone? thanks!

 

[45yearsagasman]

Do you have any motorised valves on the system? Probably in your airing cupboard. Pics would help.
View media item 44939
View media item 38425Something like theses? Don't assume it's the thermostat that is the fault.

 

[Newby2]

Yes, I have a valve like the 1st picture. I turned on the advance water on the control panel and the boiler fired up. Then after 10min I turned the advance water off. However the boiler keeps working as it should be (the heating programme is still on). A quick question: if the thermostat is faulty, will the boiler keep firing because it has no idea the required temperature has reached?

 

[Newby2]

I turned down the thermostat and it had no impact on the boiler (there used to be a click sound at the thermostat). The fire is still on.

 

[Newby2]

Now it seems the boiler fires up for 5min and then rest for 2min (while in the past this interval was much much longer), irrespective of the room temperature and not controlled by the thermostat.

 

[Deleted member 267285]

Do you have any electrical test equipment to measure voltage? It could be a sticking microswitch in the 2 port valve as mentioned by @45yearsagasman

 

[Newby2]

Is it the white box in the picture attached?

 

[Deleted member 267285]

Is it the white box in the picture attached?

Yes, but that’s a 3 port as in the second photo.

 

[Newby2]

As mentioned, the boiler has now fired up and the radiators are now warm. During this process I did not change the valve to manual position, so I guess it is not the problem of the valve?

 

[ian1182]

As mentioned, the boiler has now fired up and the radiators are now warm. During this process I did not change the valve to manual position, so I guess it is not the problem of the valve?

Did you previously hear a click when the thermostat was turned up or down and that's no longer occurring? To assist can you remove the front from the thermostat and take a picture of the wiring. Generally there will be screws top or bottom which secure the front, however sometimes they can be hidden behind the dial. If you cannot see any obvious screws take a picture of the outside and post that here.

Note be careful and turn off the boiler before accessing the thermostat as the connections may be live otherwise. If the thermostat is faulty it should be possible to bridge a couple of the wires such that the heating is active on when your programmer is in a on period.

 

[terryplumb]

As the boiler is apparently firing up for central heating ,and domestic hot water ,as selected on the programmer, what exactly is your problem ?
Is it that the boiler runs continually in central heating mode and turning down the thermostat has no effect ? If so, bridging wires at the thermostat will not have any effect.

 

[Newby2]

my problem is, the boiler did not fire up this morning when the heating became ON on the programmer (while the water is off). The boiler only fired up after I turned on the advance water on the control panel. I then turned off advance water and boiler stays on. Then it seems to runs continually in central heating mode and turning down the thermostat has no effect. thanks

 

[terryplumb]

If you turn programmer off ,does boiler continue to run / rads continue to heat ?
If so ,the mid position valve is duff

 

[Newby2]

it seems that somehow the valve gets stuck at M position, so the boiler does not fire up even though the heating is ON in the programmer. Any temporary fix? The BG engineer appointment is in 2 weeks. thanks.