Ariston SX 20 MFFICE heating pressure problem

7 Feb 2006
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United Kingdom
Hi can anyone help?

I have a combi boiler installed prior to our move in to our flat with no instructions. Its an Ariston SX 20 MFFICE.

Recently I've had to top up using the filler loop to allow the boiler to start maybe 3 times in the last 2 weeks.

Last Saturday we noticed a virbratng sort of sound when the hot tap was turned on but after a while it went away.

Then the pressure had dropped Sunday Eve and and I had to add water using the filler loop to get it to start. I kept and eye on it and later in the evening I noticed the pressure guage was reading nearly 3.5 bar. I turned off the boiler immediately and the temperature and pressure returned to normal.

Last night we were sitting watching the TV and heard a sort of whoosh (stream release sort of noise) and on investigating the boiler noticed the temp read off the scale!(over 120deg) and the pressure was nearly 4 bar. I guess now reading some posts that was the PRV kicking in!!

Does anyone have any suggestions as to what the problem could be? I am an electronic engineer so I've taken the cover off the boiler and can't see anything obvious leaking or wrong.

I've read that maybe the pump could have gone and there's a central screw that can be released to check, but I'm not sure what there is to check before I do it.

Also something about the Expansion vessle?

Any help suggestions would be good - after the weekend I had started to look in to a replacement boiler as this one is about 10yrs old, but it would be nice (and cheaper to replace parts if possible!?)

Also does anyone have an electronic manual? I've done a google search but can't find one.
Hope this isn't too waffely, but wanted to share all the symptoms!
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Ok - I've done some more investigating and I think it's the expanssion vessel that's gone. It looks relatively straight forward to change - any gotcha's I should be aware of on this model or is it as straight forward as it looks??
Think?? WHy?

See the FAQ on Boiler Pressure Problems

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