Combi with blocked DHW heat exchanger: clean or replace?

I've descaled one in a friend's baxi quite easily. If it's the primary side blocked with loose rust, that's harder to clear out.

Seconded: it's quite straightforward to descale a DHW HX secondary in situ. If the primary's blocked it's new HX time.

Buy new HX. Descale old one with dilute HCl for a couple of days, rinse and keep as a spare.

If the problem in form the primary side you'll be needing it quite soon.

Thanks, I'd more or less decided to do just that because I'd hate to find I'd killed the HX with descaler and be left without heating until I could get a replacement. Will post an update

Steve

If the primary side is blocked, clean out the whole system and then fit a magnclean filter on the CH return pipe.

It was the primary, took 25 grams out with HCl. I thought it was reasonably clean, but will give it a flush and look into filters when I have some spare time. I wish I'd got in an o-ring spares kit, the seals on the by-pass loop in particular were very tired. They seem to have a chord of 2 mm rather than about 2.25 mm as in my spares box. Yes, I know I could have stretched an undersized one but that always feels wrong to me.