boiler pressure fault

[paulwillfixit]

I'm having trouble with my combi boiler, the problem being that pressure builds up as its running, causing the relief valve to open and let water out.
When the boiler is turned off, the pressure then drops below 1 bar, which then has to be recharged to enable it to run again, which I charge to 1.5 bar.

It seems to me like an expansion problem, but i've checked the vessel, which i've discharged and repressurised to 1 bar, as it specs in the manual, and bled the whole system to make sure there's no air in.

Any ideas would be appreciated!

 

[mickyg]

If you've properly checked the expansion vessel(see FAQ) then you probably have a blockage in the pipe to the expansion vessel. What model is it?

 

[ddraig]

i've discharged and repressurised to 1 bar, as it specs in the manual

Make sure the system in not under pressure when you repressurise the vessel. pump up the vessel to required pressure with system at 0, then fill system and re-check.

 

[paulwillfixit]

I dropped the pressure to zero, before pressurising the expansion tank to 1 bar.

The boiler is a eurocombi (ariston) probably about 15 years old by my reckoning.
Not at home at the moment, so don't know the model number off the top of my head.

I was thinking it could be a blockage, there is a bleed on water pipe to the expansion tank, which water sprayed from when I opened it.
Could it not be a blockage elsewhere in the system?

looking at some other threads, people have mentioned a leakage between the domestic water and central heating in the heat exchanger.
Could this possibly be the problem?

Another mentioned is a leak at the water inlet/loop, but I can rule this out, as when the heating is switched off, eg overnight, it doesn't constantly pressurise, only when running.

 

[ddraig]

It could well be a blockage as Mikyg said, it would most deffinatly be where the expanssion vessel is connected to the pipe leading to the system, drain the boiler crack open the nut on vessel and check there, usually blocked with crud, if its not then yes you may have a split diagphram in the vessel.

 

[paulwillfixit]

I would have thought the diaphram is alright, as surely you would get water in the air when you discharge it at the valve?

i'll have a go at diconnecting the vessel and checking for sludge.
Boiler is in a small, built in cupboard, so will have to be removed before I can get to the vessel. Argghh!!

Thanks for the adivce.