FER Falcon combi- boiler problem sorted

If there were a small hole tween air and water then I think the water would get into the air - gravity would be involved, depending on the position of the hole.

If the PV had been overcharged by the bicycle pump (say to 1.8 bar), then the expanding water pressure would have to go quickly to that figure - it has to expand.

If the pv had been pumped to 1 bar but it had a lot of water in it, then the reduced air volume, when the water expands would give an extra-rapid rise in pressure.

Also - possibly relevant, we don't know the CH system volume which could be high, or the effect of the pump on the pressure guage reading, on a Fer.

As a matter of interest (cf surge tanks and accumulators) how is the diaphragm arranged in a boiler PV? Is it a balloon fixed at the water entry point, or at the air entry point, or is it a flat mambrane crimped in with the vessel's seam?
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is it a flat membrane crimped in with the vessel's seam?
I think the above. I'm sure I've seen a drawing showing that somewhere, and it's the logical cheap way of constructing them. The CH water clearly has access to bare steel in the PV (hence rust) which confirms the above. The other sort of balloon shaped diaphragm applies to potable water applications.
My take on this subject of pressure rising from 1 to 1.8 bar is that the pressure vessel may be a little undersized for the system. If I am not mistaken these are a 'compact' combi and as such may need assistance from another vessel if fitted to a larger system.
The system pressure when cold is 1.3 bar (not 1 bar as previously stated and the MI recommend 1 to 1.5bar). With the central heating turned on the pressure rises to 1.8bar and the MI confirms that this is within acceptable operating tolerance (pressure rise of approximately 0.5bar). The Fer boiler is part of the Ferroli range but no longer re-badged as Fer. The nearest equivalent boiler is the Ferroli Domina 80.

There are 8 radiators in the system supplied over a three floor terrace house.
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An update and two years on! The boiler is still going strong and there have been no problems with the PRV leaking or pressue fluctuations. I guess the expansion vessel wasn't leaking after all.

I'll get it changed to a condensing boiler for efficiency savings next year but the boiler is still serviceable and is now 8 years old. :D
It was only Chris H who thought you might have a problem!

The rest of us thought it would be fine.

Your boiler will easily give 10-12 years service if you are happy with it even though its one of the cheaper models.

Again I would like to compliment you on your ernest reading on past senarios to sort out your problems.

blimey kick a man while he is down, if i was on this forum 2 years ago i would have agreed with chris,, i've re pressurized many expansion vessels only to go back weeks or months later when they have lost there pressure,, likewise i've re pressurized many and they have been ok...you just never know but chris was right to point it out as it can happen.
There is a little trick you can use though!

With the system pressurised let ALL the air out of the EXV if it has the valve at the top.

If there has been any leaking then some water will come out even if only at the last moment.

If no water comes out then I am happy to advise client that repressurising will probably be successful.

Sorry- I didn't mean to sound big headed or indeed arrogant. Just really making the point that I didn't get any further leaks and thought that I would share this with the forum members. However, I concede that you are right, this doesn't necessarily mean that all expansion vessel problems can be resolved the same way.
ill try that,, i generally tend to stick the foot pump on and top it up,, then go home and pray :LOL: :LOL: especially if the boilers not in a utility room or loft and you have take the damn thing off the wall to replace vessel as the customers don't like a vessel fitted outside boiler in there kitchen :LOL: :LOL: i think they look nice somewhere to hang the crimbo decs

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