Pressure loss

[Megaflo-Experts]

Customer's sealed heating system is losing pressure from about 1 bar to zero overnight. Pressure rises to 2 bar when heating is on.
No water was discharged from the PRV and no other major leaks.
Expansion vessel is still at 1 bar (same as 2 weeks ago).

The pressure rises very quickly when topping up and also drops very quickly when releasing from PRV. Also tried releasing water from a drain valve downstairs and again the pressure dropped quickly.

I have noticed an AAV hidden away is leaking very slightly and wondered if that could be causing the drop in pressure, but thought it wouldn't drop that quickly.

In draining off less than half a litre of water, the pressure dropped from 1 bar to zero, in an 18 rad system?
Does this sound right?

 

[mikegas]

did you check the ev with the system full or drained? also not a good idea to keep opening the prv as they tend not to reseat

 

[Megaflo-Experts]

I checked the EV after releasing the pressure from the system. Strange thing is that after re-pressurising the system to 1 bar the EV pressure was the same - I expected it to be slightly higher!

 

[diamondgas]

Personally I'd consider the pipe/supply to the expansion vessel ... Not an insul,t but, do you know how to charge the exp vessel? What boiler are we talking about?

 

[Gray0689]

You don't need to lose a lot of water for pressure to drop

 

[collyboy]

Hi 18 rads what size of expansion vessel ??

 

[Megaflo-Experts]

Personally I'd consider the pipe/supply to the expansion vessel ... Not an insul,t but, do you know how to charge the exp vessel? What boiler are we talking about?

No worries, I normally release the system pressure and pump air into the vessel until it reaches 1 or 1.5 bar, depending on MI.
There are 2 potterton (prima 60) boilers.

 

[Megaflo-Experts]

Hi 18 rads what size of expansion vessel ??

18l
It's been working fine for 10 years! All rad get hot and circulation seems fine.

 

[Megaflo-Experts]

You don't need to lose a lot of water for pressure to drop

Thanks. That what I'm beginning to suspect, but on an 18 rad system, I though it would be a few litres at least.
I guess I could do the physics and work it out!

 

[diamondgas]

Thanks. That what I'm beginning to suspect, but on an 18 rad system, I though it would be a few litres at least.
I guess I could do the physics and work it out!

Just today re-pressurised a baxi platinum, 12 rads. collected about 8Ltrs of water.

Took less than a cup full to reduce the original gauge pressure from 2.5 to zero .... I'd emphasise the importance of keeping a drain or prv open whilst pressurising the exp vessel and waiting until the water stops draining .... Is this how you re-pressurised ... ?

Reason I harp o about it is coz its a basic mistake many make And don't know if this is the method you use ....

 

[Megaflo-Experts]

I'd emphasise the importance of keeping a drain or prv open whilst pressurising the exp vessel and waiting until the water stops draining .... Is this how you re-pressurised ... ?

The EV is at the top of the whole system so after releasing the pressure there is no pressure against the EV. I even unscrewed it to make sure the pipework wasn't blocked.
Good point about about allowing air into the system to equalise the pressure in the EV.

2.5bar to zero in 1/2 a cup! - I now appreciate it doesn't take much leakage for the pressure to drop; somehow I always expected it to be more!

 

[mikegas]

You could drain a radiator and then refill without venting the radiator will act as a temp expansion vessel if it still drops you know it's a leak or ask them not to use the system over night

 

[diamondgas]

Good point about about allowing air into the system to equalise the pressure in the EV.

2.5bar to zero in 1/2 a cup! - I now appreciate it doesn't take much leakage for the pressure to drop; somehow I always expected it to be more!

Truth is my friend it can take a heck of a lot of pumping up to remove the water from the 'relaxed' bellows of the EV and then expand them to the mi's recomended pressure .. as mentioned in took a good bucket full of water pumped out to get the EV re-charged!

 

[Megaflo-Experts]

Mike, I did ask if they could refrain from using the heating for a day, but not too keen with the current cold weather!

I reckon it could well be the AAV! Not quite dripping, but today noticed it was always moist!
Will replace it later this week and see how it goes. Will report back.

Thanks everyone for all your help and advice.