New Indirect Hot Water Cylinder Connection Leaking

[Monkey Wrench]

Yesterday I had a very frustrating day installing a new indirect hot water cylinder which the customer had bought from Screwfix. There were six connections in total (cold feed, boiler flow & return, Surrey flange with feed to shower and DHW) and, as is the usually the case, every connection needed modifying.

However, I have been unable to get a leak free seal on the boiler primary flow connection to the cylinder which comprises of a 1" MI with 22mm compression to the cylinder 1" FI thread. I have used three different cylinder fittings (I know that shouldn't be necessary but I had to try something), thread sealant, PTFE and tightened as far as it will go but still the connection weeps slightly. The cylinder FI thread is tight and all three MI fittings I have used were tricky to get the thread started but it is definitely not cross threaded and the fitting loosens and tightens (with the aid of a wrench) without a problem.

I've never had this problem before and I am at a bit of a loss as to what to do next so any helpful advice would be much appreciated. Thank you

 

[clarky101]

I use hemp & paste on all cylinder male fittings.....just belt n braces for me...

 

[Monkey Wrench]

Thank you for the post clarky101. I had considered hemp but haven't used it before and so didn't have any in the van. Which part of the connection would you use it on, around the cylinder 1" MI or around the 1" copper cone that goes into the MI connection (or both) ? Thanks again.

 

[ShaunCorbs]

Thank you for the post clarky101. I had considered hemp but haven't used it before and so didn't have any in the van. Which part of the connection would you use it on, around the cylinder 1" MI or around the 1" copper cone that goes into the MI connection (or both) ? Thanks again.

On the threaded stub and use paste on compression

 

[Monkey Wrench]

Thank you ShaunCorbs

 

[ShaunCorbs]

Thank you ShaunCorbs

Do you know how to apply hemp ?

 

[Monkey Wrench]

Apply small amount of paste to thread, Tease the hemp out a bit and then wind it around the thread starting at a 45 degree angle ! That's a guess but is that correct ?

 

[oz-plumber]

Apply small amount of paste to thread, Tease the hemp out a bit and then wind it around the thread starting at a 45 degree angle ! That's a guess but is that correct ?

Not by my standards!!

Rough the thread up a bit, apply the hemp, then put paste on, rub paste in with thumb ( this also insures that hemp is grabbing on the roughed up thread ) sometimes we smear a little paste inside the female thread - depending on how dry the thread is, and then do the fitting up.

Never have applied paste to thread prior to putting hemp on - it make the hemp spin on the thread.

 

[Stigster]

You could try Loctite 55 sealant thread on the male 1" fitting. It's a bit like hemp and boss white seal but a little less messy and the stuff has never failed me. Here is a link to the product.

Loctite 55 Thread Cord 150 Metres | Buy Now at gasproducts.co.uk

 

[Worcester]

We use Loctite 55 and 577 and don't get leaks

Same procedure as for hemp from oz-plumber

Alternative you could have considered is a taper male iron here's a screwfix link for convenience Pegler Prestex PX42 Male Compression Taper 28mm x 1" | Compression Coupling | NoLinkingToThis

 

[macackau]

Gas PTFE on joints which have given me problems works for me.

 

[Best]

Put the correct amount of ptfe tape on and use a few extra wraps on the final threads towards the cylinder on female and towards the fitting body on male and you should never have problems. But do use paste as well as it both lubricates the joint therefore letting more tape into it and obviously it also fine seals the joint.
If the fitting doesn't start to feel tight to turn with a spanner when half way on, then remove it and redo the ptfe tape as there isn't enough.
Boss White is excellent paste for non potable joints.

 

[jonnyswamp]

If I've read it right, the cyl tapping is 1" female, if so don't use a tapered thread unless the manus state you can (most I've fitted state parralel only)
Use a flanged fitting and wind your hemp/ptfe as normal (with paste)then pile up the hemp/PTFE just in front of the shoulder/flange, this should tighten up against the female fitting and seal
Don't know if I've explained it very well, but always works for me
Fitting will be similar to this

 

[Monkey Wrench]

Thank you for all the posts.

I hope I haven't confused things but the fitting on the cylinder is a 1" MI to which I have fitted one of these which has a tapered/flanged copper end that inserts into the 1" MI cylinder connection End Feed Straight Union Cylinder 22mm x 1"

 

[jonnyswamp]

Forget what I said then, didn't think the fitting you linked to in your post was compatible with a standard MI, need to be what I always called a boiler union
I've usually used a FI to 22mm comp str with ptfe or boss white and hemp, failing that, use a shorter FI fitting and put a fibre washer in the fitting to tighten up to the MI thread on the cyl

 

[tamz]

Wrap the cone with ptfe (10 - 12 turns) and tighten it on.