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Radiator Valve Replacement

Postby acsimpson » Fri Apr 17, 2009 3:16 pm


I have a radiator with the lockshield valve which has lost it's head. It was sheared off due to some heavy handed spanner work. Unfortunately it is currenlty closed and so unless someone can tell me a simple way to adjust the valve in it's current state I will need to replace the valve.

The system is an unvented s-plan with a greenstar (24i) boiler installed in the loft space. The advice on the site says to get a plumber in to do work on sealed systems. Is this a legal requirement or simply good advice due to the higher risk of getting wet while working with a presurised system (or another reason I have missed).

Assuming that there is nothing legally stopping me I have enough experience of plumbing to make me think I can do the job and wonder if someone could confirm my plan should work.

1) Switch off central heating system
2) Drain heating system (Unfortunatley the drain point is at the bottom of a different downstairs pipe run)
3) Open bleed valve on radiator whose valve needs replaced and loosen valve compression nut.
4) Catch remaining liquid which will drain from radiator and pipework.
5) Replace valve with identical replacement from DIY shed.
6) Close bleed valve and drain cock.
7) Introduce inhibitor to the system via a removed bleed valve on bathroom towel rail.
8) Refill system and bleed radiators. Refilling to 1.5 bar once radiators have been bled.
9) Run system for at least 2 hours and bleed radiators as required.
10) Increase presure as required to maintain 1.5 bars.
11) Over the following few days keep bleeding if required to remove all air from the system.

Assuming that I am not crazy to attemt this myself is there anything I have missed.

Thanks in advance for all your help.
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Simply Build It

Postby plumbbob » Fri Apr 17, 2009 8:48 pm

I don't see why anyone with some plumbing experience can't change a rad valve, it is not that difficult. You could drain the system as you describe, but most engineers would not bother to go to the trouble and cost of a complete draindown.

If I was doing it, I would.

1. Turn off boiler and vent pressure via the relief valve.

2. Shut down all radiator valves and feeds from boiler (can't remember if
Greenstar has them).

3. Lay polythene around valve and cover with large dust sheet.

4. Prepare new valve ensuring it is "off".

5. Undo existing valve and catch any spurts of water. When dryish, quickly remove valve and fit new one.

6. Open all valves. Re-pressurise. Bleed rad involved.

Test and go home.
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Postby rosebery » Fri Apr 17, 2009 9:02 pm

No your list is pretty comprehensive and there is absolutely NO reason why you can't do it yourself.

Couple minor points though. 1. You should only need to bleed once. The system is filled from "the bottom" with a combi and thus you should get no airlocks. 2. Buy your replacement valve from your local reliable plumbers merchant NOT from a "shed" unless you want it to shear again LoL. 3. Add inhibitor via a rad (unless the towel rail has a blanking plug) and when the system is just about full. Undo the blanking plug at the opposite end from the bleed valve. Connect a ½" x 15m elbow so that the 15mm part is pointing ceilingwards. Just pour the inhibitor in.

No you ain't crazy - go for it.

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Postby htg engineer » Sat Apr 18, 2009 10:03 am

I would replace as you have described.

htg engineer
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Postby acsimpson » Sat Apr 18, 2009 9:29 pm

Thanks guys you've confirmed what I thought. I guess my plumber shopped at a shed :-O

I've had a couple of rads off and drained when decorating so probably best to add inhibitor but I'll try plumbob's plan of not draining it all down. (Except I'll already be home). :-)

I'll let you know how it goes.

I know a regular service schedule is a must for anything gas, but do you know why it's said to be even more important on a sealed system?
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Postby acsimpson » Mon May 11, 2009 9:09 am

I finally got around to changing the valve this weekend and like usual there were a few hickups but I got there in the end. I accidentaly over filled the system to 2 bar rather than the 1.5 where the guide needle is on the presure gauge can someone please let me know if I should reduce the presure or if 2 bar will be fine as I suspect?

The full story goes as follows.

It all went well until I took the new valve out of the packet and realised it wasn't compatible with the existing tail. A quick trip to a DIY shed later (they were all that was open) I had the valve and work continued.

After spending half an hour draining the system I gave up and reverted to shrouding the valve with towels and just pulling one off and putting the other on.

Next the blanking plug on the radiator was too far in to fully screw a 15mm elbow in and after trying in vain to find a 15mm straight coupler in my odd bit box I found a reducing elbow which combined with plenty ptfe made a good enough seal with the elbow pointing up. I tested it with water which of course meant I could no longer fit my full litre of inhibitor in so I had to open a compresion joint in the loft and add the rest.

Once presurised and bled all that was required was a slight tightening of the new tail and all seems fine. Except that I was a little tired and turned the refil stop cock the wrong way taking the presure up to 2 bar rather than 1.5. (I assume this will be fine as everything I can see suggest 3 bar is the acceptible maximum.
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