CHanged a TRV by creating a vacuum - a few things.....

Hi all

I changed a TRV today (I know it's not cold at the mo but my mates has been faulty for ages - it was only the one and when I turned the heating on and removed the head it heated up!! - so obviously the sensor head was faulty).

I inserted 2 bungs (15mm and 22mm) inside the F & E cistern in the cold feed and vent. It is the first time I have used these before.

I have a few questions though to clear up if possible:

Before I could turn the lockshield valve fully off, I had to loosen a small thin nut just below tbe head of it. What is this for, is it to secure the valve nut to the spindle?!! Anyway I did that and loosened the valve at the other end, into a drianing kit I have which has a 15mm collar that fits around the pipe just below the valve and allows the water in the rad to drain into the box (like a cat litter tray size)!

The vacuum I had created in the system by bunging it obviously worked as no water came from the rad valve. I loosened the nut holding the valve to the 15mm pipe and installed the new valve (I used the original nut and olives that were on the pipe and rad tail). I tightened up, took the bungs out and the rad filled up. After bleeding the rad about a minute later water came out of the air vent and the F & E cistern was no longer filling.

So the TRV was changed correctly... After heating again the rad was hot and there were no leaks ... but something I found a bit strange, when I removed the old TRV body the pipe it was attached to moved up and down a bit (like it had a bit of give) below the floor... is this normal? it seems fine now with no leaks? Just wanted to be sure!

Also the bungs I used-the rubber part is a bit squashed now!! Are they re-useable after shaping like this ...??

Last point-the new TRV head I have (it is a different make to the original)-screws on but I have only done it hand tight (very tight though). It doesn't come off. Is this OK?

Thanks for any help/info

the pipework isnt clipped under the floor hence the movement, its not an issue.

the bungs should be reusable until the rubber starts breaking up, ive had mine for 7 years.

the trv head doesnt need to be overtight. hand tight is fine. as long at it operates correctly leave it as it is.

The thin nut under the lockshield valve spindle will be the gland nut. It compresses the gland packing against the shaft to keep the water in.

Usually they don't need to be touched, but if the valve hasn't been moved for years it may have stuck.

It is usually only necessary to nip up the gland nut a bit if the gland leaks.

If the gland leaks with the nut fully tightened, you may have to add a bit to the packing under the nut to seal it.

it was only the one and when I turned the heating on and removed the head it heated up!!

Click to expand...

That's what it's supposed to do.

Thanks for your help. It's a gland nut like a tap has, like a stopcock.

I had to loosen it a turn or so to turn the lockshield head off!

Can you recommend any good bungs? I got mine for £1-30 each from BES!! Any better quality ones out there? The rubber has got thicker now after being used and hasnt returned to its original shape! Still OK though I hope?!

Also, the bung insidenthe cold feed didn't feel as tight as the one in the vent! But obviously it worked! Probably felt loose as it was under water!!

For a good quality bung kit, try the 'Drayton Drain Easy' kit. They're a bit more expensive than you BES ones, but should last a lot longer. I have some Draytons, they are v. good quality rubber.

Available from B&Q and plumbers merchants.

http://www.diy.com/diy/jsp/bq/nav/skins/popups/scene7.jsp?skuId=9275079