Heating Pressure Loss

[paulcurtis]

Hi all,

This pressurised system was installed about eleven years ago, and most of the existing radiators were replaced. For some years, the system has slowly lost pressure. I have put a sticking plaster over this by injecting a leak sealer into it, then re-pressurising, which works for a season, and then the issue returns.

This winter I thought I'd try and find out more, by isolating sets of radiators. Long story short, I found the radiator that is affecting it. I don't even need to isolate it to stop the loss, I merely need to turn it off, and leave the balance valve open.

However, there is no sign of leakage. The radiator is downstairs, and one of the 'new' ones, and is in very good visual condition. But clearly when this radiator is turned on, and gets hot, the pressure drops. I am not sure if the pressure drops when the entire system is cold. I don't think so.

I can only think of two possibilities:

1) There is a minute crack at the top of a radiator, which opens when hot. As water seeps out and runs down, it evaporates en route.
2) It isn't the radiator, it is the pipework feeding it that gets hot and leaks, The pipes vanish into the concrete floor. I don't know where they join, although I can take an educated guess.

Any other ideas please?

 

[Last Plumber]

Hi all,

This pressurised system was installed about eleven years ago, and most of the existing radiators were replaced. For some years, the system has slowly lost pressure. I have put a sticking plaster over this by injecting a leak sealer into it, then re-pressurising, which works for a season, and then the issue returns.

This winter I thought I'd try and find out more, by isolating sets of radiators. Long story short, I found the radiator that is affecting it. I don't even need to isolate it to stop the loss, I merely need to turn it off, and leave the balance valve open.

However, there is no sign of leakage. The radiator is downstairs, and one of the 'new' ones, and is in very good visual condition. But clearly when this radiator is turned on, and gets hot, the pressure drops. I am not sure if the pressure drops when the entire system is cold. I don't think so.

I can only think of two possibilities:

1) There is a minute crack at the top of a radiator, which opens when hot. As water seeps out and runs down, it evaporates en route.
2) It isn't the radiator, it is the pipework feeding it that gets hot and leaks, The pipes vanish into the concrete floor. I don't know where they join, although I can take an educated guess.

Any other ideas please?

I cannot say they are impossibilities but more likely in my experience is the packing gland on the rad valve leaking when it is open. That too can evaporate and leave no sign.

 

[paulcurtis]

I cannot say they are impossibilities but more likely in my experience is the packing gland on the rad valve leaking when it is open. That too can evaporate and leave no sign.

Thanks for the fast reply - this is the nut directly under the lockshield cover I assume?

 

[Last Plumber]

Thanks for the fast reply - this is the nut directly under the lockshield cover I assume?

Yes. try to 'nip' it up. Not too tight, just nice!

 

[paulcurtis]

Yes. try to 'nip' it up. Not too tight, just nice!

Yes, will do, many thanks.

 

[paulcurtis]

Yes. try to 'nip' it up. Not too tight, just nice!

Regrettably, I don't think it's the gland. As I previously said, having the lockshield open but the TRV turned off does not result in a pressure loss. I have removed the TRV head and the lockshield cap (hidden screw under an insert!), and reversed things - so the TRV is open and the lockshield closed, and there is still no pressure loss.

I am wondering if a joint within the concrete floor is weeping, when hot. So I think I will isolate the radiator, but bypass it with a pipe connecting the two flows, with a restrictor to increase or reduce the flow. If it still loses pressure, clearly, it is pipework. If not, I am completely flummoxed.

Any more ideas, please?