On Sunday, June 13, 2021 at 8:14:57 PM UTC+1, Tim+ wrote:
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?
Well, it could do. Without the radiators acting as a €œheat sink€�, the heat
exchanger is probably running hotter, especially if your HW system relies
on a simple thermo-siphon to circulate the water to your HW tank.

Actually, that is a fair point - thanks.

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...
Sooting isnt good. Suggests inadequate air supply but a certain amount in
an old open vented boiler is probably normal. A good clean out and
sweeping the chimney wouldnt go amiss!
Tim

Yeah - we had similar kettling issues a couple of years ago and my service guy
had to do a lot of soot cleaning, although no-one ever understood quite why
it was so bad. Covid restrictions have meant that we didn't get
them in last autumn. As I mentioned, I had separate reason to take a look
inside a month or so ago. The thermocouple had burnt away and the pilot
light was quite yellow. I replaced the thermocouple and cleaned the jet of
the pilot light (about as far as I would go on my own). At that point, the flames
were pretty clean and I didn't notice any great excess of soot. So it ... feels ...
like this sooting up has occurred quite quickly.

Maybe I will (as a temporary measure) try leaving some rads on as an
experiment.

Useful Tim+, thanks.
J^n