Glow worm fuelsaver 30 b cuts out

Hello
I have a Glow worm fuelsaver Mk II 30B which runs 5 rads in a two storey house, and an indirect hot water cylinder.
There is a lot of pipe work because the boiler is a long way from the hot water cylinder, although this may not be relevant
I suspect the boiler is gradually scaling up because it bangs and cuts out and I have to relight the pilot. Due to money and time restraints I have had to delay fixing it and I am still hopeful that it will respond to a flush and descale. (Am I allowed to mention brand names of flushing compounds here?)
What happened over time is that I found I could reduce the banging and frequency of cutting out by reducing the boiler thermostat to the minimum setting, and by setting the boiler to heat the water only and not the radiators, (I live here alone and seem to have developed some strange habits)
I have been able to keep the system going until now, when it has started to cut out again, after only cutting out maybe once or twice if at all in about a year.
In fact it cuts out within a few minutes of relighting, from what I can see the knob that you hold in while igniting the pilot comes out a certain distance on releasing thumb pressure, until the time of cut out when there is a click and it comes out a fraction more.
I want now to get a suitable descaling compound and flush it out but will I have problems getting the boiler to stay alight long enough for the descaler to work? I know it has to run for 48 hours, not a few minutes as it has been doing, what I mean is, if I can drain the system and refill with the descale compound will the descaler start to work cold just enough to improve the circulation to stop the boiler over heating and cutting out, or is there a chance that the drain and refill will help get some of the sludge out of the boiler?
Many thanks

have you checked the basics eg that your pump is ok etc?

A descaling product does not need to have the boiler alight/heat to make it work, although as with most chemical reactions heat makes it faster, but you will need the pump to work to circulate it.

Make sure the descaler you use is suitable for a copper heat exchanger which I believe this boiler has.

The strongest one available I believe is Fernox DS40, but this is so powerful it could leave you with leaks in the system!

What ever you choose to use make sure you follow the M I's exactly.

Thank you
This sounds encouraging!
The pump is definitely ok, but there may be other checks I should make, I am not a heating expert. There could be a fault in any of the devices attached to the boiler, safety cut outs etc, I suppose.
Actually, I am not sure it is copper, when you scratch the water pipes with the fins attached, it shows silver, I suspect it was aluminium, but I will check with the makers.
I feel inclined to go for a stronger descaler rather than a weaker one, and if it opens up leaks, so be it.

I believe the over heat stat on this works by cutting out th pilot light which is why you here the 'click' 30 secs or so after the pilot has gone out. It is ths pilot gas valve shutting.

Don`t be looking too deep at first . Does everything heat up in a reasonable time and get hot enough.. If so change boiler stat first it may just be getting too hot causing noise and overheat stat to trip

I don't think there is a 30sec interval. the knob jumps out a few mms with a click, at the same time as the pilot goes out

Yes thats prob right thinking about it again

Hello namsag
Is the boiler stat the adjustable knob that the user uses to control the boiler temp and shut down, or is there an internal one as well? And is there a safety cut out that I could check for cutting in (i.e. out) too early?
Actually when I was running the ch it did take a long time for the hot water to circulate, even when I was able to run the boiler at level 6. Up until now, when it seems to be giving out completely, I had to run it at level 1, almost completely off!
I know there is some scale because I once had to clean out the pump, but I am grateful for any pointers to eliminating the easy faults first.

Hmmmmmmmmm...

I just managed to light the pilot again and decided not to turn on the main supply and see what happened, and after a few minutes the pilot went out again.
Is it theoretically possible for there to be so much scale in a boiler that just the heat from the pilot is enough to overheat it?
By the way I stripped it earlier today and cleaned aout the cooling fins, which were a bit clogged but not too bad. No soot, just a white deposit with a sulphur type smell. Didn't do it any good.
After gradually getting worse over the years , this particular developement seems to have come on suddenly.

I doubt it. I think you may be looking at an additional fault here. Could be faulty overheat stat/thermocouple. I think these are all linked together on this boiler. namsag could be correct in his assumption. Scaling up may be a side issue here.

I changed the thermocouple about two years ago with a "universal" part.
I can't remember what the symptoms were at the time, but I think it was more like no pilot at all, whereas now I can sometimes light it. If you propose changing it again then I'll give it a go, is there any way of verifying failure of these parts?
I don't know about the overheat stat, what is that? Should I be asking the manufacturers tech support for specific details?
I have some free time on tuesday and will get back to the forum after speaking to t s.
Thanks for advice

Yes, if thermocouple gone then it would usually not work at all. I wasn't sure if this was type that linked in series with overheat stat, but obviuosly not. Overheat stat will be clipped to pipe work in boiler and connects to interupter via 2 wires (where then thermocuple screws in)

OK, thank you gas4you.
I think I have to decide what to do next before I ask any more questions, ask t.s. advice from manufacturers, replace parts, descale or update boiler for a condenser maybe.
And in the meantime I relit the boiler yesterday and it has inexplicably remained alight up to this moment!

gas4you said:

have you checked the basics eg that your pump is ok etc?

A descaling product does not need to have the boiler alight/heat to make it work, although as with most chemical reactions heat makes it faster, but you will need the pump to work to circulate it.

Make sure the descaler you use is suitable for a copper heat exchanger which I believe this boiler has.

The strongest one available I believe is Fernox DS40, but this is so powerful it could leave you with leaks in the system!

What ever you choose to use make sure you follow the M I's exactly.

Click to expand...

DS40... I like your approach. Must be used with upsost respect but boy does it work.

Kicks every power flushing machine into touch.

DS40 can be used with most heat ex's.

Its so bad, that it comes with a free wallet now that was in the Pulp Fiction Film.

Dave