Cleaning a heat exchanger from a combi boiler

[Keith D]

Is it possible to use some chemical to remove limescale from the inside of a direct hot water heat exchanger from a combi boiler or is it a case of replacement?

[John Rumm]

I seem to recall someone on this group having some success pouring through a concentrated solution of Fernox DS3...

Can't hurt trying can it?

[.]

'cept when it burns through the diaphgram and leaks into the bath/sink/kettle :(

( has happened )

[John Rumm]

Still no more bu**ered though is it? ;-)

[.]

yes, goes from an operable system to one that's a callback.

on a sat afternoon, owner with 3 small kids. no engineers available for 50 miles or 2 days... BiL responsible .... :(

[Doctor Drivel]

[Ed Sirett]

Yes, there is a small risk that the unit will then leak between the primary and domestic sides. Suggest dilute HCl - available as brickwork cleaner from Builders Merchants.

[Andrew Gabriel]

Me, probably. Worked fine.

Eh? You will be running it through that side anyway.

[John Stumbles]

I've used that with success, pumping through with a garden sprayer and putting the used dilute acid back in the sprayer bottle to pump through again, testing by chucking a bit of bicarb in and seeing if it fizzes, adding more HCL as necessary. Took all day though. For the next one I'll try to get the heat exchanger out and use Kilrock (formic acid) which seems better at dissolving limescale (and is recommended for such jobs)

[Ed Sirett]

I had assumed that the unit was already removed.

[John Stumbles]

I've done the next one now and about 2 hours and about a pint of kilrock got it all flowing nicely. I'm sure it's not 100% descaled but I had other stuff to get on with there, and I've got to go back to fit a scale inhibitor anyway so I'll probably give it a second helping then.

There was no way[1] I could get the heat exchanger out but it was easy to pump in the kilrock via the filling loop supply valve and out again by a washing machine hot valve (or I could have used the kit sink hot tap) so I did it in situ. The descaler working its way through the pipework to the other taps etc was probably no bad thing either! It's a bit of a pain tipping it back from the bucket into the sprayer and pumping it up again though: I think I'll look at one of those small submersible water-feature pumps with all-plastic & ceramic impellers etc next time. Unlike power-flushing I reckon you don't need much flow: just enough to keep fresh descaler moving through the works.

[1]to a first approximation: numpty had boxed in the boiler with umpteen screwed panels etc and I CBA to dismantle it all.