28mm rubber washer for cold water tank connector?

3 Oct 2006
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United Kingdom

I have a new cold tank which has a 22m tank connector for a feed for a shower pump and a 28mm connector for the cold feed to a vented hot water cylinder..

The 22mm connector came with a plastic outer washer and a rubber inner washer and sealed perfectly.. The 28mm connector came with no washers at all.. I went to all 4 plumbing dealers in the area and none stocked rubber washers nor could they get any.. I tried their suggestion - a polythene plastic washer inside and out, but no matter how much I tighten this it still weeps..

any ideas? I am obviously going to have to drain the tank, and there could be some muck or something trapped between the inner washer and the tank.. but I am suspicious of the washer..

The tank instructions said definitely no 'goo' but is it worth trying some jet blue or similar? (I've heard of people using red hematite for sealing immersion heaters, could I use that? the waters not for potable use but am still dubious about using a car gasket product! :) )

any help appreciated. Only want to drain the tank once if I can help it!!


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Use PTFE on the washers and wrap it round the tap connector where the washer goes.
how did you drill the hole in the tank? is it possible you have damaged the tank slightly causing it to weep?
drill the tank ?

every one knows you heat up a bit of tube & poke it through.

manufacturers recommend it. :D :D
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every one knows you heat up a bit of tube & poke it through.

manufacturers recommend it. :D :D
Just stop that right now.

trevw, the best method of sealing is to drill a hole of exactly the right diameter, i.e. such that you have to 'wind' the tank connector into the hole. Not with it so small that it distorts the wall of the cistern, of course, but not so large that it doesn't touch the threads of the fitting.

If you can't seal it with PTFE, then I suspect you'll have to resort to silicone sealant, but the reason manufacturer's discourage this is because [they claim that] it deplasticises the PVC, thus making it more brittle. Clearly, brittle is not a good thing for a cold storage cistern to be.
Just wind a lot of tape round the connector at the angle beween the flange and the cylindrical part, to make a triangular section fillet. If the thread starts right at the angle, wind enough on that too so the nut seals on it.

Using a hot pipe, and using silkicone, are both really common methods, of which I've yet to hear causing a problem. I'd put money on them not doing so, on a modern tank. PE has come a long way!
Thanks for all the replies!

I cut the hole using a sharp hole saw and am pretty sure it didn't damage the tank, but the hole was slightly bigger than the thread (1mm or thereabouts). Next time will try and get exactly the right size hole cutter!

(Am occasionally a little clumsy so I think I will continue to leave the hot pipe method to others - would either brand my self or end up with 3 holes in the tank :))

Will try ptfe tape as described and keep my fingers crossed, then fall back on silicon if that doesn't work.. It was so close to sealing with just the washers that I am very hopeful! - Will let you know how it goes..

cheers and thanks again for the help.

Thanks again for all the help with this! I fixed this over the weekend. The hole was maybe a couple of mm clear all round which sounds like one of the main causes of my problem. It also had a bit of a 'burr' on the inside. I filed off the inside of the hole, then used a rubber washer someone I spoke to about this had spare and finally wound ptfe as suggested above to make the triangle section (this also centered the fitting in the hole). The combination seems to work fine..

next time I will make sure I have exactly the right size hole saw!!



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