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PostPosted: Thu Jan 26, 2017 11:55 am 
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Hello UHM members

I need to drain the CH system to replace a TRV. As a DIY man I don't have the freezing kit and Radclamps so I need to empty the system. Unless someone knows better.

My CH is pressurised (combi-boiler) and I also have underfloor heating in one room. I have no idea how it is all connected to the boiler, but presume that when I empty the system from the radiator outlet valve that a significant amount of water will empty due to the number of radiators(12) and underfloor heating pipes.

This whole process seems a hell of a lot of waste water, new inhibitor and all the faffing around when refilling and topping up again to get the system full again.

Any advice appreciated.

K


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PostPosted: Fri Jan 27, 2017 11:16 am 
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1. Do you have to replace the whole TRV or could you get away with just changing the head?
2. You only need to drain down to the level of the radiator. So if its upstairs, not so much of a problem.
3. Might be cheaper in terms of inhibitor / hassle to pay someone with a pipe freezer to do it.


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PostPosted: Fri Jan 27, 2017 11:40 am 
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Thank you for your comments Andy

#1 Not quite sure by your question TRY "changing the head". The TRV is faulty, max temp always.
#2 What I thought was just to drain the radiator and collect any other spillage is it occurs. With CH system off I am inclined to think no leakage from pipe where TRV is replaced.
#3 Thought has crossed my mind and depending on the advice on here.


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PostPosted: Fri Jan 27, 2017 3:41 pm 
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1. TRV's come in two parts. The valve assembly, and the thermostatic head. The valve is attached between the radiator and the system's pipework. It is opened and closed by means of a pin which sticks up out of the valve. The head contains a wax or oil capsule which expands as the room (NOT the radiator) gets hotter, and pushes down on the pin to close the valve. The thermostatic head has no water in it. It is attached to the valve body by a plastic ring or serrated, often chrome, ring. The head can be taken off with no escape of water. If the head is not connected properly, it won't push down on the pin, the valve will never close. You might try taking the head off and checking the pin. If it moves up and down (about 5 to 7 mm) against spring pressure, the chances are the valve is OK and the problem lies with the head. If the pin won't go down, try tapping it lightly with a small hammer, or similar. They can stick. If it is stuck in the down position (unlikely given the symptoms) you could try turning it gently from side to side with pliers. Don't try pulling it up - if it comes out of the valve body you will have a slight leak. If your TRV is of a type still available, buy a like for like replacement. Try changing the head only at first, and if that works, you won't have to touch the water side of things.

2. If you make sure that all automatic air valves are closed, and that no air can get into the system, then in theory your should be able to bleed off the system pressure (e.g. at the radiator bleed valve), close down the lock shield valve at the other end of the radiator, counting the number of 1/8 turn to close so that it can be opened the same amount, drain the radiator and remove the TRV with only a little water leakage. Personally I always freeze the pipes as I don't want to have to deal with a sudden escape of water if something gives. Also, some boilers have automatic air valves inside them, which means removing the cover.



For this message the author andy48 has received gratitude : Kabous
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PostPosted: Sat Jan 28, 2017 9:19 pm 
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Thank you for this information Andy. Will try replacing the head first then.

You don't perhaps know where to purchase the head. Bulldog brand.


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PostPosted: Sun Jan 29, 2017 7:40 am 
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https://www.google.co.uk/search?q=bulld ... e&ie=UTF-8

Sent from my HUAWEI VNS-L31 using Tapatalk


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PostPosted: Sun Jan 29, 2017 12:45 pm 
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Before you buy just the head, check the prices for head only or whole valve (you don't need the lock shield). Often the price difference is minimal, and if changing just the head doesn't work, you'll need the rest of the valve anyway.


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PostPosted: Sun Jan 29, 2017 12:56 pm 
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Actually was offered a new TRV by a friend who thought he had a spare one in the garage, but cannot find it.

It is definitely a faulty head and not the valve as I swapped it for another in the house that is still working as it should. Some searching on the net suggest that as the Bulldog brand is manufactured by Pegler that any Pegler head should fit. Have emailed Pegler to ask for availability.

Yes, I saw the rather strange prices for the TRV and LS pack being cheaper than TRV only.


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PostPosted: Sun Jan 29, 2017 1:21 pm 
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I'd be tempted to pop to your local Screwfix and pickup one of these. Try it, if it doesn't fit then take it back.

http://www.screwfix.com/p/pegler-terrie ... 15mm/19052

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Darren

Maidment Properties - Bathroom and Kitchen Specialists - Dorset


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PostPosted: Fri Feb 24, 2017 1:06 am 
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Update

Pegler Terrier head is a suitable replacement for the Bulldog brand. Found some on eBay, replaced faulty one, problem solved, and some some spares.

Thanks for all advice especially. Andy 48.

Anyone have advice for Easiest way to add cleaning chemical to pressurised CH system? New thread me thinks.


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