Immersion heater thread sealing?

[Tim S]

Hi,

Just before I start - what's the current wisdom on sealing immersion heater threads?

a) PTFE b) Gas PTFE c) Something funky from

I'll avoid the traditional hemp and Boss White as I'd like to be able to undo them one day without turning the cylinder into a pice of modern art(!)

Also, which is reckoned to be the best bet for smaller taper threads, like

3/4" sensor pocket doobries?

All the rest of the connections are direct to 22mm compression which is nice - less fiddling.

Cheers

Tim

[Dave Plowman (News)]

Likewise.

Only other thing I use for 'difficult' connections is Fernox LS-X which is a form of silicone. I had problems getting a seal between a copper tap connector and the plastic pipe to the toilet cistern. That sorted it.

[Dave Baker]

I just use ordinary clear silicone on everything. You do have to let it go off completely before turning the water on though. If it hasn't set then the water just forces a path through and it might as well not be on there at all.

[YAPH]

I wrap PTFE around the thread (to help with removal next time), bunching a load of the tape up against the fibre washer at the shoulder of the thread to assist the fibre washer in sealing to the cylinder boss.

[onetap]

cylinder. It didn't leak with either the old cylinder or the new one.

You get a washer with the immersion heater, which should form a seal between the two flat, clean flange faces.

I put PTFE tape around the threads to be sure. I used the virgin white PTFE gunk, on the BES link you posted, on both flange faces and the PTFE tape to be sure, to be sure. It worked for me.

[John]

I think the face should provide the seal - not the thread. Is the washer damaged?. If so - then a twisted cord of PTFE at the shoulder of the thread may work. Best to get a new washer though - and a smear of grease on the thread to ease it out in the future.

[Dave Plowman (News)]

One benefit of PTFE is it may prevent corrosion between the threads making removal easier when the new immersion fails - as it surely will. ;-)

[John]

If more people thought about the future removal then there would be less posts about how to remove things that are stuck!

I believe the purpose of the thread is mainly to provide a clamping force onto the sealing washers. Trying to seal the thread is not the best way to go. Only tapered pipe threads are supposed to be for the purpose of sealing as they tighten up to form an interference fit.

Threads have "truncated" form which inevitably leads to there being a clearance - hence leakage route around the root of the thread.

Please - think of future removal. Good clean seating faces - without damage - a new washer - and the lightest application as Dave suggests should do the trick.

[onetap]

[e-mail]...

=A0 London SW

PTFE is a lubricant, it's used as non-stick coatings. It's use makes the threads easier to assemble and disassemble, the main reason for using it in this instance. I had put the original immersion heater in 5 or 6 years ago, probably with the same method, but I do not now remember. It came out with no grief and no distortion of the cylinder boss.

[Tim S]

Tim S wibbled:

Thanks to everyone. Yes, there is a fiber washer, now that I've opened the box to look - never fitted an immersion before(!)

So PTFE tape around the thread and maybe just a smear of Virgin White on the flange faces which sounds harmless as it's non setting.

Ta

Tim

[John]

Sounds good to me. Good luck. (and for the future when you remove it - you should be okay.)

[Dave Baker]

Sealing the thread should really not be a factor. It's sealing the flange to washer interface that matters. The thread is not even designed to seal as it's a straight not taper thread. You wouldn't try to seal the threads when bolting a cylinder head to an engine block when it's only the gasket seal that matters. Put a light smear of silicone on both sides of the washer, do it up tight and leave it for a few hours for the silicone to set before turning the water back on. Bob should be your aunty's husband.

[Tim S]

Dave Baker coughed up some electrons that declared:

Regarding the thread - yes I gathered that. I think the PTFE was suggested in order to stop the metal threads jamming up over time, which seems reasonable. Couple of turns of PTFE would be enough to handle that problem.

Silicone: wouldn't that make it hard to undo?

Cheers

Tim

[Dave Baker]

Shouldn't do no. I do mean a very light smear though. Just enough rubbed into the surface of the gasket to fill any imperfections. Last time I fitted an immersion without anything on the gasket it leaked like a sieve no matter how tight I did it up. We're not really talking precision machined flanges here and frankly the gaskets are crap. A smear of silicone sorted it though.