Glowworm boiler intermittent cut out

[Bobz]

Hi,
I am not a boiler expert, but after calling an independent repairer once and British Gas (BG) 4 times to fix the boiler w/o luck, thinking of getting involved myself to try and make some sense of it.
I have a Glowworm fuel saver MKII which is 15-20 years old. After turning the CH on for the 1st time this year, it fires up for a few seconds before it makes a clanking noise and cuts out. The pilot remains on now, although had problems keeping it on a few weeks ago. The pump and the motorised valve in the attic were changed about 1.5 years ago. I have been told by BG they are both ok. BG changed the programmer. They also changed the thermostat twice, telling me that I was the unluckiest person in the world to have a new faulty stat. The second one is now not working either. BG have assured me every time that the problem has been fixed, only to find out that after a few minutes, hours, we are back at square one. Can you please help as it is getting a bit chilly at nights. Thanks.

 

[meldrew's_mate]

After turning the CH on for the 1st time this year, it fires up for a few seconds before it makes a clanking noise and cuts out

Can we assume it works OK on hot water and the header tank is in the loft and higher than the pump and valve, and that these high points have been successfully bled of air?

Your symptoms point towards acute lack of circulation at the boiler, though I would have thought even BG would have come to that conclusion by now? Hang on, you've had BG in four times and they haven't mentioned powerflush yet I don't belieeeeve it!!

Check the pump is pumping. Is there a noise which indicates the pump is pumping rather than just running. If you dismantle it you can check if the impeller is still attached to the shaft, and is not bunged up with goo.

Glowworm used to fit return filters to some of their boilers, perhaps a last resort to check this as it involves a lot of work to get to it!

Is the system sludged?

Are all the TRVs open, not stuck shut; check the pins are up.

 

[Bobz]

Thanks for your reply meldrew.
There is no hot water either. Header tank is in the loft above the pump and valve which are also up there. bg told me that there is no air in the system after trying a few radiators.
You are right about lack of circulation, i.e. the stat doesn't switch the pump on, so it cuts off, which according to BG explains the noise as there is nowhere for the heat to go.
The pump does pump when it received electricity and the radiators warm up when that happens.
If by sludged, you mean the heat exchanger, again BG checked it and say that it is clear. Also checked the valves and the pins are up.
can you explain what you mean by Powerflush.
Thanks again.