FER Falcon combi- boiler problem sorted

8 Sep 2005
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United Kingdom
Just to say a big thank you to this forum. The PRV on my boiler was dripping and the boiler pressure would rise to 3 bar when the heating was on. I searched through the forum and discovered that my expansion vessel may also be the problem.

The expansion vessel was pumped back up to the correct pressure (after draining down the system) and fresh inhibitor added. The pressure on the system is now spot on and rises from 1 bar at cold to a maximum of 1.8 bar when the heating is turned on.

Also the PRV has stopped dripping!!

Keep up the excellent work- I managed to save some money by not buying a new PRV (which costs around £70 because it includes part of the manifold also) and also managed to wire up a new wireless drayton thermostat by researching the previous posts.
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Sorry to spoil it for you, but the chances are that the diaphragm in your expansion vessel has failed. It will work for a while, but eventually the air that you've pumped in will be absorbed by the system water and the problem will recur.

The best permanent solution is to fit a new generic expansion vessel external to the boiler connecting onto the return pipework. The integral exp. vessel is probably at the back of the boiler and very difficult to replace and an expensive spare part.

Incidentally we appreciate that you took the trouble to search for your problem rather than ask us first. Not many people do that....
It has been working for over a week now and still no leakage from the PRV overflow pipe. Why do you think the diaphragm has been permanently damaged?

Surely, after a week, I would be seeing the tell tale symptoms by now.
How old is the boiler? It doesn't sound like anything that's been on the market in recent years. As for the timescale for recurrence of the problem, it might be a month, it might be a year. You will find out in due course.
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Think the falcon 2 came out in about 1999 and has been available until very recently if not currently. Curious about that diagnosis chris, what leads you to that conclusion?
Ferroli Falcon 2 (aka Fer Falcon) and was fitted three years ago. The PRV only started leaking when I was topping up the system and didn't shut off the tap properly. The filling loop is disconnected from the system as water bye-laws.

There was no water leaking from the schraeder valve and the pressure is now stable. Having reserched the forums, I am just curious why you think the diaphragm has failed. The boiler is virtually the same as a Ferroli Domina 80 and has the effectively the same parts.
Well if it's only 3 years old I'm probably wrong. It's just that I haven't heard of FER boilers being available in UK in recent years so assumed it was 10 years or more old. But you wouldn't necessarily get water from schrader valve if diaphragm had failed.

Anyway, I admit I made an assumption. I should know better.
I'll keep an eye on the expansion vessel pressure and if it fails again, I'll fit an external one as suggested.
Incidentally, there is no reference to the "Falcon" on the Ferroli website, so I'm curious to know where this boiler comes from.
Its a "second line" for sale through merchants I think.

If he had pumped up the expansion vessel WITH THE SYSTEM STILL OPEN then it would never have pressurised if there was a full scale leak in the diaphragm.

Sometimes they leak slightly at the edge seal.

Rising from 1.0 bar to 1.8 bar as suggested is too great an increase.

Should have been set to about 1.0 Bar with system open and then pressurised to about 1.5 bar. It then would increase to about 1.8 bar when hot.

Tony Glazier
Agile said:
If he had pumped up the expansion vessel WITH THE SYSTEM STILL OPEN then it would never have pressurised if there was a full scale leak in the diaphragm.
Good point, but if the leak was very slow, like a typical bicycle tyre puncture (which I know only too well), you might not notice anything at first, but presumably the air would gradually release to water until the cold pressures equalised. Then I imagine there would be a very slow (over months perhaps) migration of water and air via the leak so that the residual air would diminish and hot system pressures rise.
I am afraid that I dont agree!

In the normal system there is an equal pressure on either side of the diaphragm ( otherwise it would just move until that was the case ).

There with equal pressures there is no reason why the air should move into the water.

On your bicycle tyre there is a pressure of about 0.7 bar inside and ) 0 bar outside
I see what you're saying, Tony, and it makes sense. But, supposing the precharge air pressure is 1.5 bar (at which point diaphragm would move to fully occupy vessel) and then system pressure was raised to 1.0 bar (at which point diaphragm would continue to occupy all space, since it would still be at higher pressure), the diaphragm could not expand further to equalise pressures and a pressure differential would remain, hence leak.
Yes but if set up as i suggested at 2317 then that would not happen.

In any case even if it was wrongly set as you suggest, the leakage would stop as soon as the pressure was equalised.

the leakage would stop as soon as the pressure was equalised.
Which is exactly what I suggested. But the existence of the small hole would still allow some minimal seepage of water into air chamber and consequent air absorption. It is then only a matter of time before air loss causes a repeat of symptoms.

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