VERY LO-NG Story - Main Combi heating System. Help needed!

13 Jul 2007
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United Kingdom
So begins my sad saga.

Like most of us, I like a problem and the satisfaction of solving it and felt capable of doing so as I have had some plumbing experience (Pre Corgi) and have, in fact fitted a complete system around 20 yrs ago (Tho my mate, Bill the Plumber did the final checks)

Here begins. About a month or so ago, my 9yr old Main Eco30 Combi stopped working. No heat and no hot water.

I checked and seeing the pressure gauge had dropped, repressurised using the FIXED loop, to around 2Bar. Went round and bled the system and found a little air in the system after which the pressure dropped to about 1.5 bar. Fine for a week or two then it stopped working again.

Re-pressurised again and that lasted about 24 hours before needing to be once again Re-pressurised.

Checked a few forums and decided I needed to change the Pressure Release Valve to eliminate that as the cause. No probs as they are less than £5 on ebay. I decided to drain the whole system as the bottoms of the rads always seem quite a bit cooler than the rest (Took about 4 hours as a couple of rads are fed by micro-bore). No real sludge emerged tho.

I needed to slightly modify the pipe work to fit the kungfoo copy pressure valve as the dimensions were a slight difference, but having done that was up & running in no time.
I purposely closed both valves on the towel rail so that I could add inhibiter once I was satisfied that the problem had gone away.

After around 2 weeks felt I could safely do just that. WRONG!! A week later no pressure again??

I carried on Re-pressurising every morning whilst deciding what to do then decided to have a go at the Expansion Vessel. Took it to 14.5 PSI having found no pressure (At least I dont THINK there was) and that fixed it.
Feeling a bit paranoid, I kept looking at the gauge for almost a week before feeling comfortable and that I had finally cured the problem. Just beginning to relax and deal with other problems in life and....Wait for it...
Last week (After about 2 more weeks) it went yet AGAIN!!!!

Re-pressurised once more and that lasted 24 hours and I have had to re-pressurise it again this morning. - Ok. Now what?

I am thinking that the system is over pressurising and blasting the water past the valve a few times when it gets too hot and then eventually there isn't enough water left in the system?

From what I have read, it seems it could be a pinhole in the Diaphragm of the pressure Vessel or a small leak in the heat exchanger (Evaporating before it shows) then over heating, losing water and then losing pressure.

I feel a failure here and am now considering calling in 'The Man' as, although I could change the pressure vessel, it might not be that and an engineer can test parts that I am not able to and obviously he should be better able to spot the problem as he should know where to look.
Is it now time to hand over the reins?

Any thoughts or observations?
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Add a bottle of leak sealer to it. I've seen a few pinholed main heat exchangers on these boilers but doesn't mean yours is.
P.S. Was the prv passing before or after you changed it ?
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It seems to be a typical case of an extreme desire to DIY when it really needs a pro to diagnose exactly what your problem is.

There is really only one place to diagnose heating problems and that is in front of the boiler.

Just like your GP always likes you in front of him!

P.S. Was the prv passing before or after you changed it ?
Hi Gigz.

the PRV wasn't leaking as such but did release water before I changed it.
I would guess that there was actually nothing wrong with it.
Baxi prvs aren't that expensive, first thing I would do is remove the 'kungfoo' copy and get the genuine one fitted. Plumb center normally keep them in stock.
Also it would be a good idea to recheck the expansion vessel, do this with the boiler empty.
If you know what your doing you could disable the heating wiring, hydraulically isolate the system from the boiler and retest the boiler as an individual component. To determine boiler issue or system problem.
Yes, but did you do that with the system pressure at zero all the time you were doing that?

But before starting, did you let air out of the EXV and check that the system pressure went down?

Yes, but did you do that with the system pressure at zero all the time you were doing that?

But before starting, did you let air out of the EXV and check that the system pressure went down?

Turned system off and released pressure on outside drain cock.
pressure was zero when I re-pressurised.
No air came out of the schrader valve.
Pressure remained fine for approx 2 weeks.

Should I have repressurised THEN check for air in the Expansion Vessel before depressurising?
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