Hi,
My friend's 18 year old boiler makes a groaning noise whenever it
cycles on. The noise stops once the boiler cycles off. I am wondering
whether noise reducer gel would be beneficial in this situation.

As far as I understand it the noise reducer gel addresses the problem
of "kettling" which, supposedly, sounds like a kettle boiling
(surprisingly enough). I would not say this low pitched groaning noise
sounds much like a kettle, but it definitely eminates from the boiler
itself rather than the associated pipework or other fittings. Neither
is it coming from the pump, because as I say, it is only apparent when
the boiler is actually firing rather than just circulating the water.

So my question is, is the noise reducer gel likely to be worth the
twenty odd quid?

Thanks for your help.