leaking central heating

[Rakker]

Hi, I'm a newbie with a problem of logic I can't solve. Our sealed central heating system loses pressure fairly rapidly (from 1 to 0 in a week) when in use. I've finally narrowed the problem down to one radiator - when I close this radiator's valve, the pressure in the system keeps for 1-2 months. However, surely closing the valve only stops the flow of water but does not reduce the pressure in the pipes leading to the radiator or the radiator itself. Is the valve somehow to blame? I can't see any evidence of a leak anywhere. I'm intending to replace the valve with a TRV anyway and hope this might solve the leak, but any ideas of where the problem might lie would be welcomed.

 

[gas_man_gaz]

are you closing both rad valves off?
check that water isn't coming out of the prv pipe wen the ch is on, if it is ya need to check the charge in the expansion vessel

 

[Rakker]

are you closing both rad valves off?
check that water isn't coming out of the prv pipe wen the ch is on, if it is ya need to check the charge in the expansion vessel

Hi, thanks for the reply. No, I only closed the control valve and haven't touched the lockshield valve. I've previously replaced the expansion vessel and the PRV. I checked the charge in the expansion vessel and that is spot on. Everything seems to be functioning normally as long as that one radiator's control valve is closed, and has done so since January when I discovered this "solution".

 

[Red_Man]

tried introducing leak sealer into the system?

 

[TicklyT]

Could it be a leak around the gland nut on top of the valve that only opens when the valve is hot, but the hot valve is evaporting off the water?

Closing the valve, presents a different part of the spindle to the seal, and that part may seal OK. Also, with the valve closed, it doesn't get hot, so it may not leak.