Boiler Making Rattling Noise

[David H]

A few times now my combi boiler (condenser type) has made a vibrating noise a bit like a pneumatic drill for a few minutes and gone off again. Otherwise it is working perfectly. This time I was next to it when it happened, and it didn't stop when I turned on the hot water or turned off the heating, but did as soon as I turned off the mains and was fine when I turned it on again. Assuming there's no internal damage causing it otherwise it wouldn't work properly afterwards, what else could make it happen?

[dunnitall]

I think it's called kettling ours does it but not sure how to fix. Probably best to google and see what it comes up with.

[SirOracle]

Could be the fan , have you tried to lubricate it with WD 40?

[mastercraft]

DON'T use WD-40.

[SirOracle]

OK Mastercraft ...use any thinning oil then if you don't like WD 40.

The fan in a combi gets a fair bit of heat and the bearings dry out.

[The Builder]

It does sound as though it's coming from the heat exchanger. Build-up of sludge and/or hard water scale. Adding scale inhibitor to the system may deal with it if it's not too well established.

Otherwise, the heat exchanger would have to be de-scaled or replaced. You can hire de-scaling equipment, or there are Companies who will do it for you.

Assuming it's a gas boiler, I think I would use a "Gas-Safe" plumber, even though access to heat exchangers doesn't necessarily involve gas connections.

[JamesE]

My boiler had severe kettling. One summer I undid the drain plug of the heat exchanger and a great splodge of sludge came out (after I'd poked with a thin screwdriver, it was blocked until I did). After that I poured a bottle of "boiler silencer" in the tank. It was not very effective. Following some research I applied silencer concentrate, using a gun, directly into the system. This was very effective.

[David H]

I'll check up kettling and come back. It's not pipes banging, the one in my old house did that till they were properly secured, but this is a regular rattle deep inside the unit which has only happened a few times in the last year or so, the boiler's maybe 7 years old now. But it's had two boards replaced already which blew (one turned off the hot water, the other the heating), and works perfectly at last. But if the rattle is a portent of trouble ahead I would definitely go and get it fixed to avoid worse happening. I have a firm at the top of the road who charge a bit but do a good job so if it starts complaining more I'll have to bite the bullet and let the moths out of my wallet again.