Boiler pressure - heat exchanger?

emmjay123

Hi

Hoping to get a second opinion here on our boiler issue. It's a Worcester Bosch condensing combi. Symptoms are pressure dropping back to zero within minutes of refill, and at the same time a flow of (warm) water out the condensing outlet. Plumber isolated the boiler to confirm issues was with the boiler and not a leak in the central heating pipework.

Plumber believes the heat exchanger is kaput and either it or the whole boiler needs replacing. 

Any thoughts of agreement or disagreement much appreciated before we go ahead with a very expensive repair. 

Thanks
Michael 

Bendy_House

Hi Michael.

Very clear description - thank you - and the plumber has done the obvious tests.

He isolated the boiler, so the pressure loss (a serious one...) is from within the boiler. Three possible routes out from the boiler; (1) is a leak that's peeing out all over your room. It ain't that. (2) is a trickle from the safety discharge pipe, which would indicate a 'letting-by' valve and the pressure having increased too high. It ain't that. (3) is a leak from the system water into a part that lets this escape out the condensate pipe. And that is essentially the mainX.

So, yes, pretty conclusive.

Which exact model WB is it? And how old is it?

Many models have had known issues with mainXs corroded or cracking, something they just should not do at all. The mainX ('engine') should really last the life of the boiler, well in excess of 10 years. Following a spate of such issues from a few different manufacturers, often caused by using aluminium (I presume an unsuitable alloy) for the mainX construction, many (most? all?) boiler manufacturers now offer a 10 year warranty for their boilers, to restore confidence.

So, you 'may' have a good chance of a goodwill payment/FOC repair from WB.

coffeehound

How much do they say the repair would cost?

emmjay123

Thanks Bendy_house, sounds like you know your stuff. The boiler is around 11 years old now so unfortunately outside of the usual WB 10 year heat cell warranty. We will likely replace rather than repair as the part alone comes in at £700.

Bendy_House

Yes, surely replace rather than repair.

I'd like to think that most manufacturers have this issue sorted now, but many still insist on using 'aluminium' for their mainXs. I can only hope that they have a found an ali alloy that is fully resistant to acidic condensate, and the not-uncommon 10 year warranties given out these days would suggest they have fixed these issues. (I'm assuming the condensate was the issue, but have also heard of ali exchangers 'cracking'.)

I'd still - personally - rather have an SS exchanger. Ours hasn't given a moment's bother in 16 years. (Every other part has, tho'...)

Belenus

Bendy_House said:

Yes, surely replace rather than repair.

I'd like to think that most manufacturers have this issue sorted now, but many still insist on using 'aluminium' for their mainXs. I can only hope that they have a found an ali alloy that is fully resistant to acidic condensate, and the not-uncommon 10 year warranties given out these days would suggest they have fixed these issues. (I'm assuming the condensate was the issue, but have also heard of ali exchangers 'cracking'.)

I'd still - personally - rather have an SS exchanger. Ours hasn't given a moment's bother in 16 years. (Every other part has, tho'...)

Is your boiler a bit like Trigger's Broom?

It is still the same boiler even though almost every part had been replaced.

Bendy_House

Yup :-(

It's running well, tho'...

Ohmagawd! I've just remembered - the mainX was replaced too! The guy who'd done a repair on another part found that the CH water flow was not as free as he thought it should be. He discounted everything else, so reckoned the MainX was full of sludge. So he replaced it...

Afterwards i told him that I was on a one-pipe system, largely consisting of 15mm pipe. The look on his face was a picture...

I'm ashamed.

(Yes, it was a fixed price repair.)