How do you drain the radiators when you have a combi

[geordey]

I have a VAILLANT VCW GB 242 EH Combi boiler with inverted loop radiators downstairs.

I want to put thermostatic valves on every radiator and move one radiator to a different wall downstairs. I will need to drain the system but as it is closed at around 1.5bar? how do I drain and refill?

 

[BentheBoatie]

doesn't matter whether it s COMBI or other, somewhere in the house will be one rad (down stairs) with a drain cock on it. its usually near the front or back door.

attach hose to spigot, undo square nut with a multi key / spanner and drain to outside of house.

this will in theory release all water above this point, though there will undoubtedly be a few spots around the system with little pockets left.

when you have changed the valves (buy good ones!) refill using the filling loop (stainless steel braided hose) under the combi boiler which has check valves at either end (both need undoing). close valves when pressure gauge reaches 1.5 bar. you'll need to leave at least one rad bleed valve upstairs open while you do it to allow air to escape

good luck!

 

[breezer]

I want to put thermostatic valves on every radiator

you should not do that, you must leave at least one rad with no trv to act as a bypass, most commonly it is bathroom rad

 

[keego]

doesn't matter whether it s COMBI or other, somewhere in the house will be one rad (down stairs) with a drain cock on it. its usually near the front or back door.

That might be the case on your planet but here on earth it's not always like that.

 

[geordey]

Thanks BentheBoatie,

Found the drain points and turned off the feed to the heating (leaving water supply intact). Drained using garden hose.

Your advice V useful and job done without spillage.

I realised I have an extra expansion tank to play with and was able to refill and pressurise the system to 1.5 bar afterwards.

Thanks again.