There must be a leak but can’t think where

[John.g]

That's good news really even though it doesn't say much about the longevity of the EV, I think Zilmet pre charge with nitrogen, also I think every external EV installed should have a isolation/drain valve, (I have seen them advertised somewhere) as it makes it a very simple operation to check the pre charge pressure without system drain down, I wonder how many are checked on the annual service?.

 

[Anj]

That's good news really even though it doesn't say much about the longevity of the EV, I think Zilmet pre charge with nitrogen, also I think every external EV installed should have a isolation/drain valve, (I have seen them advertised somewhere) as it makes it a very simple operation to check the pre charge pressure without system drain down, I wonder how many are checked on the annual service?.

John you are an absolute star.

I didn’t realise there was such a thing as an expansion vessel service valve (I’ve seen loads of external EVs fitted but never seen that valve used). Draining a massive system and losing £30 of inhibitor each time is just painful - just seen one on the Screwfix website... definitely going to add that!!

Thanks even more.

 

[Anj]

John you are an absolute star.

I didn’t realise there was such a thing as an expansion vessel service valve (I’ve seen loads of external EVs fitted but never seen that valve used). Draining a massive system and losing £30 of inhibitor each time is just painful - just seen one on the Screwfix website... definitely going to add that!!

Thanks even more.

to report back.
System has been pressured for 2 days now (All valves Open) and no loss of pressure so it would seem the problem was the expansion vessel. I suppose in hindsight it was obvious if I have isolated everything but the EV and the pressure still dropped. [Still a bit mystified why a PRV hadn’t popped], but misunderstanding of how to properly test an EV threw me for a loop.

Added the service valve and must agree with John.G why this is not fitted as standard is a shame.

I’ve learnt a lot:
1. Definitely only way to check an EV is with no pressure on the water side... pressing the Schrader is only one test and not enough.
2. A 2 year old EV can still fail
3. Had a recap on Boyles law and how to calc the pressures on an EV
4. That there is such a thing as an EV service valve and should always be fitted with an EV
5. Gate valves are rubbish (although mine seem to be OK for now) but I will change them to 1/4 turn ball valves.

Huge thanks to all those responded, particularly John.G

 

[Donametchi]

What boiler do you have?
Any AAVs?
If you leave it for a few days does it continue to drop?

This is the simplest and more accurate remark.
Remember it,s a pressurised system,So once the pressure has been se to 1.5 bar of pressure it should only increase to around the 2bar mark once the heating is on.If you are finding a pressure drop and no wet ceiling marks you can only have a weep on a fitting under the floor so get a head torch and wriggle like a mole under the floor and find it.But before doing this check your radiator tails downstairs with dry paper towel as you would appear to have a very slight leak.Good luck