Expansion vessel kit male connector appears to be very slightly less than 15mm

[kez1]

Hi,

I just fitted a wall mounted 25L expansion vessel to the heating circuit of an oil fired combi-boiler.

The machined 15mm male inlet connector on the expansion vessel kit is connected to a female 15mm compression nut with olive and plenty of PTFE tape. The female compression join comes from the boiler. I put as much PTFE tape on he olive as I could get on it.

This was all fitted last week, and I managed to get the compression nut tight, and the join leak free at operating pressure, without any problems then.

The day before yesterday I noticed the compression nut had started to slide off the expansion vessel male fitting. It was clear this had happened because a ring of the white PTFE tape had been left behind in the original seating position. I was able to wiggle the compression fitting up and down slightly, which had not been possible when I had fitted it days before. I think I got to it just before it blew off.

It can't blow off now because of the cable ties in place, but it's dripping a bit.

I think the male inlet to the expansion vessel is slightly less than 15mm. If so, and it's faulty, I'd rather just fix it if a permanent fix is possible.

Any ideas?

 

[aptsys]

The machined 15mm male inlet connector on the expansion vessel kit is connected to a female 15mm compression nut with olive and plenty of PTFE tape. The female compression join comes from the boiler. I put as much PTFE tape on he olive as I could get on it.

What's the reason for the PTFE over the olive? Did you try without it first?

I suspect you've put enough on that you've not actually compressed the olive into the fitting. There shouldn't be any need for PTFE.

 

[dilalio]

Bit of paste... hand tight... then a ‘nip’ or two... pressurise... check... another nip if necessary... heat up system & pipework... check again whilst hot... and nip again if necessary... do not graunch (over tighten)... it’s a touchy-feely thing

 

[Jackrae]

Teflon tape creeps, just like a snail, that's why it's banned in most industrial control systems.
Use too much, put it under pressure and it'll (sooner or later) creep out of a joint
When first produced it was marketed on the basis that it was a thread lubricant, not a thread sealer.
Somewhere in the depths of history, less than wary individuals decided to use it as a sealant and from there the myth has grown.