replacement insulation panels also
Yes.
I'll explain the diagnosis so that you can all laugh at me
But first I'll try and excuse myself by saying that replacing the boiler at some point has been on my long to-do list since moving here, just due to age and relatively low efficiency, and I had wanted to avoid the cost of getting a pro to fix anything as it was going to be chucked out anyway...
The boiler was losing pressure. This is my first combi boiler; I didn't know how much pressure loss would be considered normal. My first thought was to look for leaks, and indeed I did find some very dubious weeping joints (and I've just found another one while removing a radiator to decorate behind it). There could have been more of the same hidden under the floors. So I would periodically prise up a new bit of floor and look for drips.
Then I heard about other possible causes of pressure loss: leaks inside the combustion chamber and expansion vessel issues. One suggestion was to pressurise the boiler to above-normal pressure, close the boiler isolation valves and wait for a bit. If the pressure drops, the leak is inside the boiler. I did that, an *no pressure drop*. OK, time to check the expansion vessel (and I actually posted about this on this forum); as suggested by someone here I checked the pipe connecting the expansion vessel to the boiler and it was blocked. Problem solved, I hoped! But no. Maybe it was repeatedly re-blocking itself. Seemed unlikely, but it would be easy enough to fit an external expansion vessel in the airing cupboard. Did that, and actually the problem was still getting worse.
So at that point, I blah blah blah and there was a lot of very obvious green and white corrosion on the heat exchanger and water damage to the insulation panels.
As suggested above, it is possible that it is actually from washers rather than the heat exchanger itself; certainly the damage is to the sides or maybe mostly to one side.
So it clearly needs some professional attention - or replacement.
