New PRV but still venting at 2 bar

[Xen]

Hi everyone,

I'm looking for some advice. Our boiler began losing pressure recently and it turned out it was venting through the PRV. Brand new PRV was fitted but we're still losing pressure. I noticed it was still venting from the PRV again even though the boiler was only showing 2 bar of pressure (still in green zone) so I don't know why it should be doing that.
I'm going to get a different plumber to look at it but I wanted to get an opinion so I don't end up just having parts thrown at it again and hoping for the best. Could it really be overpressurised and the gauge is just broken? Just a dodgy new valve fitted? Anything else?
The boiler is a Greenstar 24i system, probably about 11 years old. I've topped it up and given it another run - it was showing about 1.2 bar cold, rising to pretty much bang on 2 bar before the PRV vented again.

I'm not sure if it's related (although we've had this problem since we moved in 18 months ago well before the boiler started playing up,) but our hot water cylinder also drips fairly often from the 3 bar valve to the outside pipe (Megaflow CL250). I've tried restoring the air pocket as per the instructions on the side of the cylinder, but it doesn't last long at all before it's dripping again. I'll get that fixed at the same time so any advice on that would be good too.

 

[Madrab]

I noticed it was still venting from the PRV again even though the boiler was only showing 2 bar of pressure (still in green zone) so I don't know why it should be doing that.

If it's the standard and correct PRV rated @ 3bar for that boiler and it's still lifting @ 2 bar then chances are it's the gauge that's wrong.

Can a new PRV be faulty, yes but I'd be tempted to investigate the gauge too. While you're at it get someone qualified in to service the unvented.

 

[yorksbuilder]

Expansion vessel kaput?

 

[Johntheo5]

It should be relatively easy to check the actual pressure by installing a pressure gauge at the filling loop (left hand) system connection.

 

[Xen]

Expansion vessel kaput?

Possibly - the pressure difference between hot and cold is quite a jump. But I still wouldn't expect the PRV to vent when the gauge is reading only 2 bar so I think there might be another problem

 

[yorksbuilder]

Worth checking the expansion vessel anyway

 

[Johntheo5]

IF that boiler has a external EV, then, next time the pressure reads 2.0bar check the schrader valve air end pressure with a tyre pressure gauge.
Don't know what capacity EV is installed but any size from 10L up should be fine.
With pre/charging pressures of 0.75/1.25bar, a 10L EV will accomodate a Hot system vol of 116L at 2.0bar and 180L at 2.7bar still below the 3.0bar PRV set value.

 

[Xen]

IF that boiler has a external EV, then, next time the pressure reads 2.0bar check the schrader valve air end pressure with a tyre pressure gauge.

It has an internal one, but the schrader is accessible - it pokes out of the top of the boiler on this model. Unfortunately whoever installed it ran the return pipe immediately above it so you can't get anything on it! (the same installer who mounted the magnaclean so close to the ceiling that you can't actually open it to clean it...)

 

[Harry Bloomfield]

The gauge must be reading low, check the pressure with another gauge.

 

[Madrab]

Expansion vessel kaput?

It may be but pressure should show to be up @ around 3 bar if the EV was causing it. A 3bar PRV should start lifting around 2.8bar, especially a new one.

Gauge needs checked IMO

 

[Xen]

Turns out the EV is kaput and also the new PRV was dodgy.
The top mounting for the EV is accessible which meant I could loosen it and rotate it to be able to get to the schrader, and that leaked water. I fitted a new PRV of the same part number, and that has been in a few days now, and my jug on the outlet is still dry.
So for now I have pumped some air in to the EV, though I know this will get dissolved. I have some space in the airing cupboard so I will get a remote EV - it'll give more capacity and stability anyway, and better than having the boiler taken off the wall to replace the integrated one.

 

[Johntheo5]

Glad to hear you've found the problem.

You might consider purchasing and installing one of these on the new EV, saves draing down the system when/if checking the pre pressure or renewing the EV, around £20, I've installed them on 2 EVs I've recently replaced on relations oil fired systems.
You might also bleed any remaining air off the present EV, otherwise it might be a bit confusing if after installing the new one that the system pressure changes due to a air leakage on the now redundant original .