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[Help] Not Another Plumbing Advice Thread : Plastic to Metal Thread Sealers



M

marlowe

Well-known member
Dec 13, 2015
3,936
Another plumbing diy job has cropped up so soon after the radiator one (which I haven't yet gone back to finish).

This time I need to change the inlet valve on a toilet cistern which is straight forward enough. My question is regarding sealing the plastic pipe thread to metal nut (olive?).

I've done a bit of research and the general consensus seems to be to use something called "pipe dope" as opposed to ptfe tape. As you can see by the photo it appears that this has been used before. So I need to remove that and clean that off before reconnecting.

What are the pitfalls that I need to avoid and what is the best "dope" or sealant to use.

The problem is there is no isolator to the cystern so the water will have to be turned off at the mains. So on a practical level the thread sealant I use will have to be able to be exposed to water fairly quickly as I can't keep the mains off for any extended length of time so any sealant which needs to be kept dry while curing is not that practical.

Also what is the best method /product to clean the old gunk from the metal thread which will be reused.

Toolstation do Tru Blu and Boss. Both have good reviews so I'm thinking of opting for Tru Blu unless advised otherwise.

Edit: just noticed the first photo is sideways so anticipating the usual wise cracks along with [MENTION=205]Tom Hark, Preston Park[/MENTION] 's inadvertently sensible advice.

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M

marlowe

Well-known member
Dec 13, 2015
3,936
Tom Hark said:
Worry not OP, Tom'll Fix It :thumbsup:

Have you tried turning it off and on again?
Click to expand...

Thanks for bringing that to my attention as it may have been something I would have overlooked. I will now certainly do that with the mains. Thanks for averting a potential flooding disaster. Your advice is invaluable as usual. I'll keep you updated on the radiator thread as soon as I get back to that job and let you know if your advice proved to be as good as you hadn't intended.
 


Tom Hark Preston Park

Tom Hark Preston Park

Will Post For Cash
Jul 6, 2003
70,215
marlowe said:
Thanks for bringing that to my attention as it may have been something I would have overlooked. I will now certainly do that with the mains. Thanks for averting a potential flooding disaster. Your advice is invaluable as usual.
Click to expand...

A pleasure as always. Others may well provide valuable advice, but only Tom'll Fix It is able to provide invaluable advice :thumbsup:
 




SIMMO SAYS

SIMMO SAYS

Well-known member
Jul 31, 2012
11,717
Incommunicado
marlowe said:
Thanks for bringing that to my attention as it may have been something I would have overlooked. I will now certainly do that with the mains. Thanks for averting a potential flooding disaster. Your advice is invaluable as usual. I'll keep you updated on the radiator thread as soon as I get back to that job and let you know if your advice proved to be as good as you hadn't intended.
Click to expand...

Are you related to [MENTION=451]BensGrandad[/MENTION] by any chance?
 








M

marlowe

Well-known member
Dec 13, 2015
3,936
SIMMO SAYS said:
I believe BG's dad was a plumber so I'm sure he will give you advice. My advice would be get a proper plumber in. The two jobs you have described could be a real pain.
Click to expand...

I didn't realise the NSC BG contingent spanned four generations.
 


SIMMO SAYS

SIMMO SAYS

Well-known member
Jul 31, 2012
11,717
Incommunicado
marlowe said:
I didn't realise the NSC BG contingent spanned four generations.
Click to expand...

Joking aside the nut looks like it could be cross threaded. That will mean a new bottom entry :eek: ball valve. I would cut the copper pipe back and fit a braided flexible connector incorporating a valve for control.
 


M

marlowe

Well-known member
Dec 13, 2015
3,936
SIMMO SAYS said:
My advice would be get a proper plumber in. The two jobs you have described could be a real pain.
Click to expand...

Pain in what respect? Changing the inlet valve is relatively straight forward as I've done similar before without any problems. My only concern this time is the metal to plastic thread connection and ensuring it doesn't leak. What problems do you envisage I will encounter when making and sealing that connection?

Edit: sorry just seen your last reply which was posted while i was typing this one.
 




M

marlowe

Well-known member
Dec 13, 2015
3,936
SIMMO SAYS said:
Joking aside the nut looks like it could be cross threaded. That will mean a new bottom entry :eek: ball valve. I would cut the copper pipe back and fit a braided flexible connector incorporating a valve for control.
Click to expand...

Thanks, that makes sense as I don't like not having an isolator valve because if anything did go wrong turning the mains back on would be a bit of a problem. This is why I wanted to make sure and cover all bases before I commited to doing anything.

I was planning on replacing the bottom entry ball valve anyway as that is where the leak is coming from. That joint doesn't actually leak at the moment.
 




BN9 BHA

BN9 BHA

DOCKERS
NSC Patron
Jul 14, 2013
21,561
Newhaven
marlowe said:
Pain in what respect? Changing the inlet valve is relatively straight forward as I've done similar before without any problems. My only concern this time is the metal to plastic thread connection and ensuring it doesn't leak. What problems do you envisage I will encounter when making and sealing that connection?

Edit: sorry just seen your last reply which was posted while i was typing this one.
Click to expand...

When you buy a new inlet valve spend a little extra and get one with a brass tail.
The photo you have posted the tap connector with brass nut is cross threaded on the plastic inlet valve tail ( Simmo Says has mentioned this )
Also buy an isolation valve and flexible tap connector.
 




R

Rowdey

Well-known member
Jul 7, 2003
2,537
Herne Hill
bn9 bha said:
When you buy a new inlet valve spend a little extra and get one with a brass tail.
The photo you have posted the tap connector with brass nut is cross threaded on the plastic inlet valve tail ( Simmo Says has mentioned this )
Also buy an isolation valve and flexible tap connector.
Click to expand...


The brass shank Fluidmaster is actually about 90p cheaper than the plastic version in Screwfix.. :mad:
 






Wrong-Direction

Wrong-Direction

Well-known member
Mar 10, 2013
13,426
Nottseagull said:
What size pipe feeds the cistern? If 22 mm you don't need to turn off the water at the mains (use gate valve instead). If 15 mm, then why not fit an isolator valve beforehand? The ones without handles are quite cheap.
Click to expand...
There's a lot wrong with this

Sent from my SM-A600FN using Tapatalk
 






SIMMO SAYS

SIMMO SAYS

Well-known member
Jul 31, 2012
11,717
Incommunicado
bn9 bha said:
A little knowledge is dangerous - some advice an old boy once gave me. :smile:
Click to expand...

The problem I found was when younger I always thought a job would go easily with my dad thinking the opposite.
As I got older I realised my dad was normally right.
The loose radiator on the wall would turn into draining the system and trying to get fixings on a dodgy crumbling wall.
Then when refilling it would get an airlock which would take longer to get rid of than the original job took.
On testing the system I would find it would need re-balancing to get that far flung radiator in the back room to work.
The customer of course would say 'it always worked before' ------yeah right???
Obviously with pressurised combination boilers this is less likely to happen.
However there are still thousands of old fashioned heating & hot water systems out there.

@WrongDirection always prices jobs on the worst case scenario now.
In the rare case all goes smoothly he will realise he has nailed the firms best pair of adjustable grips under the floor and have to go back to get them :smile:
 
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