Ariston Boiler losing pressure

[superfrank]

Hi,

I have an Ariston Clas HE 30 Combi boiler that is around 5 years old and it is losing pressure daily, I top it up to around 2 and overnight it drops to around 0.5 and if you leave it will eventually drop to 0 and boiler will error.

The reason for this is because water is escaping overnight through the pipe outside, I have checked this with a bag. When the boiler was serviced in the summer a new PRV was fitted so I'm pretty sure it's not this.

The plumber seems to think this will be the expansion vessel, but to replace it is a £3-400 boiler off the wall job.

Could it be anything else and what is the best course of action, he did also mention he could try re-pressurising the system beforehand but there was no guarantee this would work.

Thanks

 

[MANDATE]

If the water is escaping from the pipe outside then the PRV is not fully closed.It will most likely have been opened at some time and there will be sediment on the valve seating face.
The options are to either clean the valve (easier said than done) or replace with a new one.
The root of the problem however most likely stems from the expansion vessel. It has a rubber diaphragm and is supposed to be pre charged with air so (like a car tyre) to give the max amount of air, This air gets compressed when the water in the system expands and normally the air and water pressure will rise around 1bar.
The expansion vessel over time will have lost some of its pressure.
You may well have a vessel which is half full of water before any expansion takes place. the result of this means the reduced volume of air when compressed sends the pressure sky high, but as soon as 3bar is reached the PRV operates.
So first action is to sort out the vessel. make sure it does not cantain water and its pressurised to 0.8bar then pressurise the water side to 1bar
Sometimes its the pipe connecting the vessel to the system that gets blocked and the extra water has nowhere to go except through the PRV
The alternative to replacing the vessel if its completely bust, is to leave it where it is and fit another one. Daughter has one hidden over kitchen cupboard and connecting pipe is copper in lieu of rubber.

If the PRV is accessible it may be possible to dismantle in situ.
To do this though you have to have a special spanner, it has to be thin (about 2mm) and when the head if the valve is raised it may not be a hexagon. mine is 'round' with a 'cut out' slot so a 'C' spanner had to be made.
I did however manage to dismantle it and clean it up, but only realised later that I could have removed the head without removing the valve

 

[superfrank]

But the PRV valve was changed about 4 months ago, surely it can't already be faulty?

I wouldn't have the confidence or knowledge to do anything you mentioned so looks like I'll be calling out a plumber!

 

[gigz]

If your expansion vessel is goosed the new prv will have blown off, it's supposed to do this, you could put a new one in every day and it will do the same thing. Get the vessel sorted and as said clean/replace the prv and it should be ok.

 

[superfrank]

Ok, so does £3-400 sound reasonable for a new expansion vessel that includes taking the boiler off the wall etc.?

 

[MANDATE]

Well if water is escaping from the outside pipe where else can it be coming from. You could try opening and closing the valve and see if it improves. It's not that the valve is worn, it will be sediment stopping it from seating.
The advice is replace the valve or clean it, but make sure the expansion vessel is operating correctly first. Otherwise you'll be back to square one.