OT need help with combi boiler pressure
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I have a ariston class he 30 boiler approx. 18months old. The pressure on the boiler keeps going up, today it has been 3.5 bar. I have released water from a radiator to bring the pressure back down but it comes back up. I have turned off both taps that fill up the tank, but it still goes up. The vessel does not have a valve to put any air back in. I have drained the system today, but to no avail. Any advice would be great. Thanks

Sounds like your vessel has gone :(

They don't die, they just get faster!

I'm surprised that your vessel doesn't have a point to recharge (you could have used a tyre pressure gauge to see how much air, if any was in there. If water came straight out you would know straight away that the vessel had pin holed) it but a lot of them do lose the air/pin hole. Does the pressure just build when the boiler is on then drop when it switches off/gets cold? If so I'd say it's most likely the vessel which isn't really too hard to change (dump the water in the boiler, take it out, put the new one in then fill him back up ) Or you could just put an external vessel on somewhere in the system.
Another thing it could be is that a filter is blocked somewhere.. but this would make the boiler just heat up to 80? then it would blow off pretty much straight away.
I personally don't know much about ariston but when I come across the problem of pressure going up to over 3bar, it's 9 times out of 10 the vessel that's the problem.
I hope this helps (:.


I've just checked your make/model online, is this the vessel you have? if so the point is at the top as you can see from the photo, if it's not I might have got the wrong part number :(
http://www.totalboilerspares.com/ourshop/p...ION-VESSEL.html

Edited by Shauna on 8th May, 2013.

They don't die, they just get faster!

passing fill valve when shut, and or both of them passing slightly creaping the pressure up check them out or replace them, there are a lot of hung wang ball valves on the market.

the reason the gibbon plumber fitted fill point to the drain side, usually you have low mains pressure.

there should be an overload valve dumping excess pressure in the event of the above ?

hope this helps

Could be the plate heat exchanger. If it bursts between heating and water then it will pressurize the heating. Turn a hot tap on and see what the gauge does.

Unfortunatly there not a great boiler

13.95 1/4 mile on a 2.95 fd. Carnt be that hard to beat!

I also thought the vessel, but can I find it no!! it has completely disappeared if it was ever there before.

When turning the hot water the gauge does nothing.

I could phone ariston as I have a 5 year warranty, but they would say to get an engineer out, looks like I will have to do that anyway.

You can't find the vessel? If it is one of those round ones I'd guess it's hidden behind everything at the back.
If the plate had pin holed inside (I've never seen this but I guess it's possible) surely his hot water would be coming out all mucky because they were mixing?

They don't die, they just get faster!

The way to tell if it's the vessel is to run the boiler (I do it at max) if the pressure rises as it's getting hotter and then eventually blows off its the vessel because it's not compensating for the heat (hence the name expansion vessel ). If it's not rising when the boiler is off then it's likely to be the vessel. Your filling loop should always be off other than to add more water (pressure) into the system so if it's rising when cold then it will be the valves passing.
Aniston aren't great though from what I know (I deal with ones that are 10years old and more often than not we rip them out and put in a baxi/vaillant)

They don't die, they just get faster!

It is rising when the boiler is not running, so yes I agree it is more likely to be the vessel, But I can't see the vessel unless it is enclosed in the black unit within the pics below. Filling loop is always off. My boiler is only 18months-2years old and I have to say we have had no probs until now.

On 9th May, 2013 ShaunaFTW said:
The way to tell if it's the vessel is to run the boiler (I do it at max) if the pressure rises as it's getting hotter and then eventually blows off its the vessel because it's not compensating for the heat (hence the name expansion vessel ). If it's not rising when the boiler is off then it's likely to be the vessel. Your filling loop should always be off other than to add more water (pressure) into the system so if it's rising when cold then it will be the valves passing.
Aniston aren't great though from what I know (I deal with ones that are 10years old and more often than not we rip them out and put in a baxi/vaillant)

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If it's under warranty still, call them out. Don't waste your time trying to sort it yourself as you risk invalidating your warranty.

Thats the heat exchanger. The vessal will be down the back.

And if it goes up when its not running it wont be the vessal. As that takes up the extra pressure caused by the heat and expansion.

If it was gone it would be at 1.5 bar wen cold then when you run it up it would go up to 3ish in around 10mins

13.95 1/4 mile on a 2.95 fd. Carnt be that hard to beat!

as said above if its rising in pressure when its turned off its going to be the heat exchanger, call the manufacturer if its still under warrantee!

thanks, will be calling them today, have turned off the water at the mains and no rise over night.