Before I bite the bullet, and get a new boiler, maybe someone could
suggest something that I havent done to try to repair this one.
DHW (and CH) comes on for 20 seconds, cuts out, comes on after 10-20
secs, then repeats.

This points to a blockage in the DHW heat exchanger. Flushed it out.
Still the same. Fitted new DHW heat exchanger. Improved things for a
week or so.

Went back to its old stop/start routine. So filled up with cleaning
fluid (Fernox iirc) left in for a week, flushed through etc, made little
difference, and the exiting water didnt seem particulalry dirty.
So, last gasp attempt, filled with more cleaning fluid, left in for 2
weeks, flushed through thoroughly.
This also made no difference.
DHW H/E off again - clear, no blockage.

This now points to a primary heat exchanger blockage.
To try to discount other possiblilties, I have cleaned the flue, the
diverter valve insides, and other accessible parts.
Still playing up.

A new primary H/E is around £300 iirc. Half the price of a new boiler,
and it looks like it will be a swine to fit, as all the joints are
seized.

So, have I missed anything before I scrap this one?
Thanks
Alan.

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