Replace thermostatic mixing valve - what could go wrong?

TimW wrote in news:p1lk7l$1dj$ snipped-for-privacy@dont-email.me:

Just make sure the olives on the pipes are nice and clean. Presuming there are olives. It looks like you just need to unscrew the existing pipes and use the existing nuts to refit the new one. If so it is the olives that do the sealing and not the threads.

Put about two layers of PTFE plumbing (not gas) tape over the olives, covering both sides and do up till only moderately tight. Tighten more if leaks.

Not familiar with that boiler or valve, but don't forget that some water may come out of any of the pipes when you undo the unions, so proceed with due caution, plus containers and/or towels.

Personally I would remove and discard the nuts and olives that come with the valve, when you have got the valve out make sure the nuts and olives on the existing pipework are clean, and put three or four layers of PFTE tape on the male threads of the nuts, avoiding the olives.

I sometimes use PTFE-based thread sealants on this sort of thing, but there is a certain amount of art in judging the right quantity.

I'm ham-fisted and I find Boss Green pipe jointing compound much easier to use than PTFE tape.

I'm sure that somebody here once said to never use PTFE over olives. I did argue that I used to do this very successfully in a different life, but was shot down by just about every poster.

It's like me using linseed putty on plumbing. Everyone else uses it too, but it has to be called Boss White or you get flack for it.

PS do not do brass compressions up moderately, squeeze the ---- out of them or you get a lot of leaks.

NT

You're (obviously) quite entitled to do that, but the threads play no part whatsoever in making the waterproof joint. Indeed, they are bypassed effectively by the gap between nut and pipe. So, except as a thread lubricant, there is no point.

Just once, I have used a couple of wraps of thick/gas PTFE over the olive itself to stop a leak from a TRV.

Tightening the compression joint hadn't helped (it might have been overtight already, as well as being pulled a little out of square) it was only a tiny drip, the sort that might have sealed itself with crud after a few weeks, but I didn't want to risk water staining a new wooden floor, and didn't want to cut the rising pipe and have a coupler visible.

Yes, it's probably classed as a bodge, but every now and then, a bodge that works is the right answer in my book ...

Many many too many years ago I was in the loft of a house with the plumber who trained me for 5 years. From memory ........... the cold water supply connection from in the bottom of the galvanized tank to somewhere else kept leaking. He kept on putting jointing paste - it still leaked. I suggested PTFE. He called me a "stupid youth", but tried the PTFE. It worked. I never did get to shag his daughter.

Quite agree - it's the olive which needs to seal, not the threads. I would personally just put a smear of LS-X round the olive before inserting the pipe into the valve.

I would use Boss White to lubricate the threads to ease tightening, especially in a confined space.

I would never use PTFE tape on olives, anyone looking at it in the future will know immediately it was done by an amateur.

If the tape is applied neatly it doesn't show. And, I have had fitting installed by a professional which leaked. Water and chipboard based sink units don't mix.

I used PTFE on olives in my last house. After 18 years the joints were not leaking. You were saying something ............?

My suggestion was specifically for re-used olives, mating with a different fitting to the original one. The chances of small irregularities in the original joint, or slight variations in the position of the narrow line of contact between the curved olive and the flat taper of the fitting are great. PTFE in my, admittedly limited, experience makes it less likely that you will have to grossly overtighten the nut to get the metal to flow into position.

e threads of the nuts, avoiding the

The biggest enemy of a compression joint is dirt. Clean metal to metal should seal.

It should. Some of the time it doesn't. Welcome to reality.

NT

snipped-for-privacy@gmail.com wrote in news:28627fd0-ba00-4b9e-9e33-3803bea8ac81 @googlegroups.com:

Also important to pull the pipe out very slightly before tightening. This prevents the pipe bottoming before the olive is compressed.

I hate finding set bosswhite in the threads of compression joints or immersion heaters. Sets like concrete. If you must lubricate the threads use a smear of grease or oil.