Ariston EuroCombi over pressure - urgent advise please?

[DeeBee]

Hi group and Seasons Greetings to all :-)

I think I need to replace the expansion vessel in my six year old Ariston EuroCombi SX20, but just want to check if I have overlooked something first before I try and get one before Christmas and end up paying what I expect to be a hefty price for a part I may not need.

The short version of the story so far.

Started a week or so ago with the boiler cutting out and the system pressure fluctuating from 2 - 3 bar.

So got a CH fitter out to have a look as I did not have the time and was not sure what to do et etc. He service the boiler, cleaned it out etc and told me that he believed the expansion vessel had just lost its pressure. He told me no water came out of the valve. He refilled the boiler and set the expansion vessel air side to 1bar. He also said he thought the pressure relief valve may be faulty. That night when I checked the overflow there was a dribble from it. Before he touched the boiler there was no evidence of water coming from the overflow. On Friday I fitted a new prv and the result is still the same.

Now tonight the system pressure was running at about only 1.5 - 3 bar, so I checked the pressure of the air side of the expansion vessel and nothing. So I pressurised the air side to 1 bar as stated in the service manual, refilled the boiler and fired it up. The pressure got up to 3 bar and the prv is dumping a small amount of water.

So my question here is have I overlooked something else (i.e. another pressure regulator of something else) or has the diaphragm one the expansion vessel damaged and thus needs replaced.

According to the service manual the exp, vessel can be changed without removing the boiler if there is enough headroom which I have, so changing the exp vessel should not be too difficult, but don't want to spend the cash if it may be something else.

Anyway if anyone can shed any new light on this I would be grateful as I need to get a new exp vessel by Tuesday for the holiday season.

Alternatively will I do any more damage if I just keep topping the system up until after the holidays?

Cheers

Duncan

[Tony Bryer]

It may be easier and cheaper to tee a standard expansion vessel into the system at some convenient point, leaving the existing one where it is.

[Set Square]

I presume that you re-pressurised the air side with the water side

*un-pressurised*?

Did you say that no water comes out of the valve?

Have you checked that the valve is not leaking air? [With it pressurised, spit on your finger and wipe it over the end of the valve. Does a bubble appear?]

If the valve *is* leaking air, you may be able to seal it by screwing a cap on the end. My impression is that these things are the same size/threads etc. as car tyre valves.

You can probably stagger through Christmas without doing anything major - but don't leave it too long. If you are constantly replacing water lost through the prv, you are diluting the inhibitor in the system.

[DeeBee]

Cheers for the replies guys, but I may have cracked it.....

found Ed Sirett's FAQ on sealed systems ans sused that last time I pressuried the exp vessel I did so with the boiler drain valve shut. I tried it again with the boiler drain left open (both feed and return to the rads sealed off with the isolation valves)

Good thought there Set Square....

It seems to be bahaving better now, and the cold pressure has stabalised at

1.5 bar (thats normal for this boiler) so maybe (fingers toes etc crossed) that sorted it. Maybe the CH fitter did the same. He did say he was not used to this boiler or maybe he was just cr@p !

We shall see what happens over the next 24 hours, but I will check availabilty / price tomorrow......

thanks again

Duncan