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Brian, Plumber
Category: Plumbing
Satisfied Customers: 869
Experience:  16 yrs. experience as plumber, including full bathroom and kitchen installations.
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Im fitting a towel radiator and have so far turned the main

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I'm fitting a towel radiator and have so far turned the main radiator valve off and have capped the trv valve. I now need to change the valves to straight valves both non trv. How do I do this without the water flooding? Do I need to drain the whole central heating system? I have a modern house with condensing boiler and flexible pipes rather than copper. I'm hoping there's a way of just isolating the radiator pipes I'm working on rather than drain the whole system.


Brian :

No sorry you will have to drain down, if the radiator is upstairs then obviously you only need to drain it partially.

Brian :

Please remember to put inhibitor in when you refill the system. Even more important if under warranty as the manafactures could refuse the warranty if there is no inhibitor. Best regards Brian

Customer: Thanks, XXXXX XXXXX sure you understood me though. I've already drained and then removed the existing radiator. I've capped the trv in case any water comes up the pipe and I've turned the normal valve off. Now I want to take the valves off and want to know how to prevent water coming out of the pipes. Do I need to drain the whole system so that no water comes out the pipes? I didn't understand what you said about partially draining?
Brian :

Hi, I understand you have emptied the radiator, you will still need to drain or partially drain the central heating system to remove the valves there will be no other facility to isolate the water. To partially drain the central heating system allow water out of the system and just keep opening the old radiator valve a little with a cloth under it until no water comes out. then turn off the drain cock on the central heating system.

Brian :

you dont have to partially drain it just means its easier to fill.

Customer: Okay thanks. Lastly, if it's only partially drained does this mean you can use a less amount of inhibitor? I have another towel radiator to fit in the en suite and would have to partially drain again and then add inhibitor again. The en suite isn't ready yet in order for me to do both at the same time.
Brian :

In theory yes but I would just use a litre of inexpensive inhibitor. Or if it wont be to long before you change the other one then wait. Or Similar

Customer: Thanks. Do I need to switch off the water supply to the central heating when draining down? Also do I need to switch off the boiler for draining. If so do I just switch the water and boiler back on last thing when refilling?
Brian :

Depending on the type of boiler you have will determine if you need to isolate the water supply. if you have a system boiler or combi boiler they are sealed so there is no open water supply to them. if you have a small header tank then yes you will need to turn of the supply to this. The boiler will need to be switched off. Refilling the boiler is either by way of a filling loop normally located near on on the boiler. If its a combi or system boiler. Or by allowing the header tank to fill. Obviously you will need to bleed the radiators and any air vents before firing the boiler back up.

Customer: Thanks' it's an ideal condensing boiler and there is a filling loop connected. Looks like its a combi boiler then? I noticed the pressure is sitting below 1 bar, probably because I have removed a radiator and therefore drained the system slightly. I have a large white tank, a small white tank and a red expansion tank which confuses me as to which type of boiler or system it is but I reckon it's a condensing combi boiler.
Customer: I think I have enough info to crack on with it now but am inclined to fit the radiators to the wall and get a plumber in to connect up! Thanks for your help.
Brian :

You have a system boiler with an un-vented cylinder. by the sound of it. If your not confident in the plumbing side then yes get someone in. its sometimes quicker in the end and should not be very expensive. I have just today fitted a towel radiator exactly the same job as you are attempting, it took 2.5 hours with having to alter the pipework. So to connect a couple of valves should not be longer than an hour all going well.

Customer: Okay thanks. I looked at a pipe freezing kit as an alternative to let me change the valves without draining but still not sure about that. I guess if I've already lost some water by removing a radiator then I'd need to refill and should also add inhibitor so prob best to go the whole hog and at least partially drain and refill and add inhibitor. Thanks
Brian :

Pipe freezing is a risky thing especially if the new valve does not fit easily or you have a problem, the Ice plug melts and it all gets messy. It also costs more than a bottle of inhibitor. What your attempting is not hard if you want to try it yourself. Drain it down fill it up bleed it and done usually.

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