Replacing leaking rad valve without draining system?

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I have a leaking valve, beyond repair. Having recently drained system and installed new pipe run and rads I don't want to drain it again! Am thinking I could shut off rad one end and drain out water. Then quickly take off damaged valve as no pressure will be on it (valve where water exits). I may get some minor leakage onto a blanket under the area. Does this make sense? Seems to to me but need confirmation in case of a flood!
 
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If it's open vented bung the header tank first, if its sealed just knock the pressure off then swop it.
 
I always knock off the pressure if it's sealed (bung it if open vent) and then rely on vacuum to snatch it... But then I do have a big-ass wet vac, plugged in and sitting next to me :D
 
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Its a one pipe system. I don't get the 'bung it' response. I have a header tank which i can switch off the main cold feed. However can't i just work quickly and take off and attach the valve?
 
A Bung in the vent pipe that overhangs the f&e tank... A carrot will suffice. If you have an isolator on the outlet from the f&e, close that off too... Belt n braces etc.
 
Its a one pipe system. I don't get the 'bung it' response. I have a header tank which i can switch off the main cold feed. However can't i just work quickly and take off and attach the valve?

Yes it is possible to swap a radiator valve on a live pipe, but not always easy if you are not an experienced plumber and always risky to carpets, flooring, etc.
You can bung the vent and feed pipes at your small heating fill tank (expansion & feed tank) and then take pressure off system using drain off
 
A Bung in the vent pipe that overhangs the f&e tank... A carrot will suffice. If you have an isolator on the outlet from the f&e, close that off too... Belt n braces etc.
What no potato ?
 
But with a carrot you eat the big end and can then see what you're doing in a dark loft :p
 
Yes it is possible to swap a radiator valve on a live pipe, but not always easy if you are not an experienced plumber and always risky to carpets, flooring, etc.
You can bung the vent and feed pipes at your small heating fill tank (expansion & feed tank) and then take pressure off system using drain off
I think I get what you suggest. I logically can see how the pressure can be that great on the valve that exits the rad. So you suggest that I switch off the flow in the header tank and block the exit from the flow to the system. If I act quickly should be OK I believe. I am not a pro plumber but can join copper/bend pipes etc. Not too hard.
 
I think I get what you suggest. I logically can see how the pressure can be that great on the valve that exits the rad. So you suggest that I switch off the flow in the header tank and block the exit from the flow to the system. If I act quickly should be OK I believe. I am not a pro plumber but can join copper/bend pipes etc. Not too hard.

You just isolate electric to boiler obviously and then block the vent and feed pipes and if any auto vents in system you should close their manual caps temporarily.
The system then should be basically sealed and once pressure is dropped from system the valve could be replaced hopefully.
Water will always escape from radiator, so use a small piece of rag into rad or rad tail as you do the swap
 

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