Boiler Losing Pressure II

[RJH]

Posted a couple of weeks back - boiler losing pressure, needing half a pint or so a day. I've checked the expansion tank and overflow, and all of the below the floor pipes. I've checked most of the others, but figure the gallon or so I've put in would have made itself known on a ceiling by now. So checked the condensate - and yup, it's losing pressure/water there. About half a pint the past day with the heating/water off.

My poorly informed guess leads me to think it could be the heat exchanger, which is likely to be expensive/new boiler. Before I call the plumber, would it be worth using a leak sealant? I don't want to wreck the system and gunge everything up for a fix that wouldn't work. There's a good few metres of 10mm pipe. But if the worst it'd do is wreck a boiler that might need replacing anyway, might it be worth a shot?

[Adrian]

In message <rn4k6s$mos$ [e-mail]>, RJH [e-mail] writes

My last boiler (non condensing) was suffering from pressure loss issues. Turned out that the expansion tank was leaking.

Adrian

[John Rumm]

I had exactly the same problem on mine. Cost me about £130 for a recon main HX, and it was a fairly simple job to swap:

Its likely to be a fairly big ask to fix a leak in the primary HX.

I think I would just bite the bullet and replace the HX.

[RJH]

Thanks - yes, checked that already. And it's leaking from the condensate pipe.

[RJH]

Many thanks - I'll take a careful look.

[Brian Gaff (Sofa]

Yes I have a friend whose old plumber put that leak sealer in and it made no difference, She got a good deal on a new boiler, only trouble now is after repeated drain downs gunge presumably from the sealant or whatever keeps causing odd things like loud noises, gurgles and some radiators not working when it was perfect with the old boiler. I'm keeping my mouth shut. grin.

Brian

[RJH]

I've had a look at an online video, the wiki, and the manual (which gives step-by-step replacement instructions). I'd strip it down first just to try to be sure - although they're nothing like as expensive as I thought:

Less than £70 for a manufacturer's part. And £35 for an ebay clone. I thought they were £400+?! Am I looking at the right thing - even the manual uses 'heat plate' and 'heat exchanger' interchangeably. Maybe they're 'cheap' because of mass production? ;-)

[Fredxx]

I have known a leaky o-ring to give the same symptoms, after the boiler ran dry and overheated.

[John Rumm]

Alas no, that's a plate heat exchange as used in a combi to heat the DHW.

(its a small cross flow water to water HX, that takes heated primary water from the main HX, and uses it to transfer the heat to the DHW without allowing the fresh DHW to come into contact with the stagnant sludgy water that circulates through the rads)

You need the main HX that takes the heat from the combustion of the fuel and transfers it to the primary water in the system. Depending on model, perhaps something like:

(and yup £400 for a new one would not be uncommon)

[John Rumm]

Depending on the actual design that could be possible, but to get a leak via the condensate drain, the water would normally need to be escaping into the combustion chamber itself, and typically O rings are on the outside of it. O ring leaks would more typically give a leak visible from the boiler's casing. (usually after dribbling all over the PCB just to add insult to injury!)

[RJH]

Ha, thought it was too good to be true!

Thanks - that's the route I'd follow. Not worth throwing too much money at it at this point.

[RJH]

Yes - they are outside on this design. It was the HX - replaced and been running now at stable pressure for a couple of weeks. Many thanks for the pointers.

[John Rumm]

Glad its sorted...

OOI, what did it cost to fix?

[RJH]

In the end I went for a new part, largely because it included gaskets and O rings and cost 'only' £280 inc. (from Warmsafe, seems to have gone up £10 since). Plus the gas leak detector spray and a round of inhibitor, about £300.

I went *very* slow/methodical, and the manual was excellent (except it included quite a few unnecessary procedures). About 4 hours start to finish I'd say, plus the time flushing the system. This video helped me out a couple of times:

[John Rumm]

That's not bad for a new one...

Well cheaper than a new boiler and a good deal more satisfying! :-)

[Fredxx]

The other thing about repairing your own is that you get to know the item, and can often keep it going many years after a plumber would call it scrap.

Boilers are comparatively simple to say, cars.

[RJH]

Indeed :-)