Replacing Thermostaic Valves!

[dave12]

I Think I'm right in saying my Central Heating is a closed circuit, as it is fed by a combi-boiler. So do I need to drain the system if I want to replace some Thermostatic valves or will the water remain in the Pipes?

 

[masona]

So do I need to drain the system if I want to replace some Thermostatic valves or will the water remain in the Pipes?

Yes the water will also remain in the pipe depending what level the drain point is...

 

[dave12]

mmm, my drain valve is probably a little lower than the TRVs, would this make a difference? Will the water stay in the pipes even if there's about 1 1/2 bar of pressure in the system?

 

[masona]

No,that okay providing you drain it completely.You shouldn't get any bar reading when the system is empty.

 

[ChrisR]

NB there's a valve in the combi which will let air in, so the water will come out given any chance!

 

[dave12]

So I Just open the Valve under my boiler and wait for all the water to come out and for the pressure to drop to '0'. Then replace the valves and refill the system with water from the tap valve thats there and wait for the pressure to rise back to 1bar? Job done isn't it?

 

[oilman]

........isn't it.[/qoute]

No, water out = air in. Trouble is, water in /= air out. You have to bleed all radiators, and, this will take several goes, filling the system, bleeding the rads. Filling the system, bleeding the rads.........

You could avoid this by being a bit daring (in case something goes wrong) and organised (to make sure it doesn't), and freezing the pipes to the radiators, shutting the valves. Removing radiator complete with valves, fitting stopends on pipes just in case. Standing radiator on end and replace valve. Then refit radiadtor.
No draining, not much reflling.

 

[dave12]

Freezing the pipes? Is that using that spray you get? Like you say could be risky if it doesn't freeze properly. But like you said I could cap the pipe, but can you get these caps for a microbore pipe?
I have 3 Radiator valves to change what would you do?

Thanks for all your answers it's appreciated

Dave

 

[oilman]

You could use a spray, ok once you find out about the "crack" indicating the pipe has frozen, and wont take long with microbore. Stop ends are available for every size pipe, but might take a bit of searching. Alternativly you can hire an electric freezer, which means you don't have to rush as the freezer stays on till the job's done. Takes minutes to change the valves, but you have to pay to hire the freezer, and time to fetch it. It may be better to refer to earlier posts and drain the system after all.