Central heating problem- Any ideas?

Stumper_2

Hello, I'm hoping someone can suggest what might be wrong with my central heating. I have an old gas boiler which runs just a few radiators. It has been banging and cutting out really badly, which I though was due to lime-scale and crud in the system. I flushed the system and added a lime-scale remover product, and hey presto, it immediately worked fine, but then the banging gradually came back and after a couple of days it was just as bad as before. Now it seems that I can stop the banging instantly by draining a bit of water out of the system (and letting it refill) but it soon comes back. It's a vented system with a little tank in the roof space. Can anyone tell me what's wrong?

Thanks

ormus

the stat maybe faulty on the boiler. if its running too hot itll bang like mad. when you introduce new cold water it cools down.
is it the pipes banging or the boiler? faulty pump maybe?

pipes banging can be the water inlet valve (ballcock) in the tank upstairs. dismantle and clean it or just renew it. they are very cheap.

Stumper_2

Thanks for your reply.
If I let everything cool down and then switch the boiler on it can start banging immediately- I think that would suggest that it's not the stats, what do you think?

It's hard to say for sure whether it's the boiler banging or the pipes that connect the boiler to the tank as the tank and the boiler are very close together. The water in the tank does sometimes get hot, does that tell you anything?

As far as I can see the ball !!!! works fine, the tank certainly refills itself if I empty it.

The pump does occasionally make a bit of a whirring sound so that is a possibility. Any other thoughts?

macman

Airlock in the system maybe? Have you tried turning the pump down one notch? Normally they have 3 speeds-what is it set on at present?

Stumper_2

I'll have a look at the pump setting when I get home tonight and see if running down a notch makes any difference.

I tried bleeding all the radiators to remove any trapped air and didn't find any- is there any other way of locating a potential air lock?

I'm starting to favour the idea that the pump is either broken or full of crud, presumably if the pump isn't circulating water properly then the boiler will overheat very quickly and that that could be what's causing the banging- does this sound plausible?

macman

You can turn the pump spindle using a screwdriver, do that to see if it is moving freely. There is also a bleeed screw on the pump.