Unvented central heating losing pressure only in winter

[Selvara]

Hello there
Can expert help me with the problem of unvented hot water( mega flow) with two expansion valves and pressure gauge losing pressure only during winter when I turn on the central heating.
I have got gas boiler Worcester installed.

I could see two radiators always have gas or no water when I bleed .
I then top up pressure to one and half bar and then bleed radiator and the check pressure and start central heating.after every two days the pressure goes to zero. When I come abs check radiators ( only two) either gas or no water while bleeding so i topup
And cycle begins.

There is no leak on ceiling or floor.
On gas engineer able to
Solve . Should I run sealant in hot water cylinders or leak Detector ?

Please help

 

[Harry Bloomfield]

Solve . Should I run sealant in hot water cylinders or leak Detector ?

No! The expansion vessel (EV) and pressure release valves (PRV) need to be checked. After refilling, before starting the heating, tie a sandwich bag, around the open end of the pipe, which probably ends in an elbow, then a second elbow, the latter pointing at the wall. Start the heating, then report back whether the bag fills with water.

 

[Selvara]

Thank you sir.
Just to make sure I understand.
Are we trying to isolate if PRV leaking by wrapping sandwich bag?

 

[Selvara]

Sorry.
Can you please tell where I have wrap sandwich bag ?

 

[Harry Bloomfield]

Thank you sir.
Just to make sure I understand.
Are we trying to isolate if PRV leaking by wrapping sandwich bag?

Yes, plus whether water is being ejected because the EV is faulty/needs pressurising.

 

[Harry Bloomfield]

Sorry.
Can you please tell where I have wrap sandwich bag ?

Over the end of the pipe, to catch any water which might be ejected, as the system heats up. Just a tell-tale..

 

[Madrab]

Top up boiler to 1.5 bar and then turn heating on, once heating is on and all the radiators heat up, keep an eye on the pressure gauge on the boiler, if it's reaching >2.5 bar and as suggested the bag outside is filling up then the boiler's Expansion vessel needs checked but that should be boiler repair 1'o'1 for the engineer. If that's what it is, then bin him and get another engineer.

Strange though that the radiator is emptying, is the system water nice and clean or is it black?

 

[Selvara]

while bleeding radiator the water is clean

 

[JohnD]

Thank you sir.
Just to make sure I understand.
Are we trying to isolate if PRV leaking by wrapping sandwich bag?

Not "leaking"

If the pressure goes up too much when the water in all the radiators is heated and expands, the Pressure Relief Valve purposely releases some of the hot water to relieve the excess pressure.

Likely it is not the PRV that is the cause of the problem.

Next time you top up the water, photograph the pressure gauge on your boiler when it is cold. Then turn on the heating and photograph it again after 10 minutes, 20 minutes, 30 minutes, and when fully hot. Then photograph it again when it is fully cold. Wild swings in pressure indicate a problem with your pressure vessel.

 

[Selvara]

Thank you all.
I have wrapped sandwich and no water.
The pressure doesn’t go more than 1 .5 bar which I topped up.
It is only winter time when central heat running, day one it is at 1.5bar and day two

 

[Selvara]

PRV is two years old.
Could the water from radiators flow back to system hence losing pressure in the system.

 

[Madrab]

No, only a leak can allow water to escape from the system, if it isn't the PRV. The only other option would be through the HEX in the boiler and out through the condensate but again your engineer should have checked that. Pinholed coil would push water into the system if the unvented was under mains pressure so shouldn't be that.

Pic 2 in the mains water to the unvented and nothing to do with the boiler pressure.

You need another engineer in who's more experienced than the last yo run through all the relative tests to get to the bottom of it for you.

 

[Selvara]

Thank you.
I have tried about 7 gas engineers.
They changed PRV. Pressure gauge and nee boiler no solution yet.
This pressure low happening only in winter when I run central heating and when the system is back to cold at night.
It takes two days to lose pressure to zero .
May need to get some leak detection.
Would leak detection detect water leak ?

 

[Madrab]

May need to get some leak detection.
Would leak detection detect water leak ?

No, not from the central heating, it only detects running water, like the cold mains.

1st place I'd start with is pressurise the boiler then isolate and start to track whether it's the boiler or the system where it's losing its pressure from.

 

[Selvara]

During summer, I kept an eye on the pressure gauge at unvented system and no central heating running, the pressure was always at 1 bar until I started running central heating.

Only when central heating is running after two days the pressure goes to zero.
I also get tick tick sound during start of central heating on two radiators.