On 13/06/2021 16:18, jkn wrote:


FWIW one reason for doing this *now* is that the back boiler has starting making
'kettling' noises when it starts up. We've fairly recently set the controller to not put
the radiators on, but I wouldn't have thought that that would have caused any such
issues? It is looking to me that the heat exchanger is really sooted up - I actually
fitted a new thermocouple, and cleaned the jet out, a month or so ago, and it seemed
fine then. I'd quite like to fix/understand that even if we do finally sort out a
new boiler...

J^n


What colour is the boiler flame? If the HE is sooting up it suggests
that there's not enough oxygen, so the flame will be yellow instead of
blue. Make sure that the air supply to the burner isn't blocked and - if
possible - check the gas pressure at the burner when it's firing.

If the boiler is kettling, that's likely to be due to scale on the
*inside" of the HE rather than soot on the outside. As JR says, there
are additives which will help with that.
--
Cheers,
Roger