Cistern part needs replacing

JDPower

The plastic thread on this part is visibly worn and slightly leaking. So two questions, is it simple to replace? And what the hell is it called so I can look for a replacement? (it's on the inlet pipe) 

(i already tried renewing the PTFE tape, just on the off chance, but made no difference) 

grumpy_codger

side-entry inlet valve

https://www.toolstation.com/plumbing/toilet-fittings/c902?page=2

If it's the connection with the copper pipe is leaking, then the thread doesn't need sealing and PTFE tape. IIRC it's some rubber washer inside that has to seal the connection of two pipes. If it fails, PTFE tape cannot help

ETA: https://www.reddit.com/r/DIYUK/comments/1gvvc11/toilet_inlet_valve_leaking/

it's bottom entry here, but the connection is the same.

FreeBear

The nuts either side of the cistern are above the water level, so the only place for a leak is where the brass nut screws on from the outside. If it is anything like mine, there will be a rubber (or fibre) washer between the plastic of the fill valve and the metal face of the pipe fitting.

Turn the water supply off - You should have an isolation valve close to the cistern. If there isn't one, it would be a good idea to fit one now. With the water supply off, unscrew the brass nut, clean up the mating surfaces (gently), and reassemble with a new washer. Don't use PTFE tape. It is a waste of time and won't seal anything. If you must use a sealant, a thin smear of Plumber's Mait on the mating surfaces is all you need. So don't go slapping it on the threads.

JDPower

FreeBear said:

The nuts either side of the cistern are above the water level, so the only place for a leak is where the brass nut screws on from the outside. If it is anything like mine, there will be a rubber (or fibre) washer between the plastic of the fill valve and the metal face of the pipe fitting.

Turn the water supply off - You should have an isolation valve close to the cistern. If there isn't one, it would be a good idea to fit one now. With the water supply off, unscrew the brass nut, clean up the mating surfaces (gently), and reassemble with a new washer. Don't use PTFE tape. It is a waste of time and won't seal anything. If you must use a sealant, a thin smear of Plumber's Mait on the mating surfaces is all you need. So don't go slapping it on the threads.

Yes, it's leaking from where the brass nut joins the plastic thread. 

So there should be a washer in the brass nut? Never spotted that when I disassembled it, but did see the worn plastic threads, so assumed that was the issue. Will open it up again and see if I can dig out the remains of the washer in there and try to find a replacement. Cheers 👍

JDPower

Ok, so finally got round to trying to fix this. Tried right size fibre washer, still leaked. Tried a rubber washer, still leaked.

So any other suggestions, or was my initial suspicion of worn plastic thread right after all???

WIAWSNB

JDPower said:

Ok, so finally got round to trying to fix this. Tried right size fibre washer, still leaked. Tried a rubber washer, still leaked.

So any other suggestions, or was my initial suspicion of worn plastic thread right after all???

What is the actual issue? Are you unable to tighten the brass nut enough without it slipping? 

As long as the plastic thread is good enough to allow the brass nut to be tightened adequately tightly, then it won't be a case of water getting past the thread, as the only part of that joint that makes the seal is the end round part of the threaded tube. 

Have you examined this closely? Run your finger along it? Is it smooth? Any damage/marks/bumps/cracks that the rubber washer wouldn't manage to 'fill'? 

And, the fibre and rubber washers you tried - they matched this round end neatly? The brass nut is presumably a 'tap connector'? Ie, when you undo the brass nut and slide it back, you are left with a kind of short, top-hat fitting. The narrow part fits inside the plastic tube, yes? And there's a collar - top-hat rim - a few mm down from the end? As I'm sure you have sussed, the fibre (or rubber) washer should sit neatly over the narrow bit, and snugly against the collar. A tiny bit of the narrow end should still stick out, and this guides the fitting on to the plastic tube, going slightly inside it. All that seem ok? And even a squishy rubber washer didn't work? Are you sure it didn't get dislodged?

Really, it should be a fibre washer that is used, but it's often prudent to add a few wraps of PTFE tape over it, or a smear of jointing compound.

Bottom line - if the end of the plastic tube is smooth and damage free, and the top-hat of the brass fitting ditto, then this should seal - provided the brass nut can be tightened adequately. Time to examine both ends very closely! Easiest option is to replace the whole inlet valve, as Grumpy says. But if there isn't any 'give' in the copper supply pipe, you'd have to find one with the same length of plastic threaded part, or use a nut on either side of the cistern wall to adjust it.

JDPower

WIAWSNB said:

JDPower said:

Ok, so finally got round to trying to fix this. Tried right size fibre washer, still leaked. Tried a rubber washer, still leaked.

So any other suggestions, or was my initial suspicion of worn plastic thread right after all???

What is the actual issue? Are you unable to tighten the brass nut enough without it slipping? 

As long as the plastic thread is good enough to allow the brass nut to be tightened adequately tightly, then it won't be a case of water getting past the thread, as the only part of that joint that makes the seal is the end round part of the threaded tube. 

Have you examined this closely? Run your finger along it? Is it smooth? Any damage/marks/bumps/cracks that the rubber washer wouldn't manage to 'fill'? 

And, the fibre and rubber washers you tried - they matched this round end neatly? The brass nut is presumably a 'tap connector'? Ie, when you undo the brass nut and slide it back, you are left with a kind of short, top-hat fitting. The narrow part fits inside the plastic tube, yes? And there's a collar - top-hat rim - a few mm down from the end? As I'm sure you have sussed, the fibre (or rubber) washer should sit neatly over the narrow bit, and snugly against the collar. A tiny bit of the narrow end should still stick out, and this guides the fitting on to the plastic tube, going slightly inside it. All that seem ok? And even a squishy rubber washer didn't work? Are you sure it didn't get dislodged?

Really, it should be a fibre washer that is used, but it's often prudent to add a few wraps of PTFE tape over it, or a smear of jointing compound.

Bottom line - if the end of the plastic tube is smooth and damage free, and the top-hat of the brass fitting ditto, then this should seal - provided the brass nut can be tightened adequately. Time to examine both ends very closely! Easiest option is to replace the whole inlet valve, as Grumpy says. But if there isn't any 'give' in the copper supply pipe, you'd have to find one with the same length of plastic threaded part, or use a nut on either side of the cistern wall to adjust it.

Yes it can be tightened enough. Everything you said about the connection, washer, assembly etc is all correct. Yet the joint still leaks. Hence why I suspected the plastic threaded pipe to start with. Neither washer had any effect on the leak. I didn't specifically check the mating face of the pipes, I just noticed it seemed generally worn. So will take another look at that.

I will add, the pipes didn't seem quite aligned - when disconnected the brass pipe was a couple of mm below the plastic pipe, so this may have deformed the mating face of the plastic pipe (I have raised the cistern a couple of mm so they meet cleanly, which obviously would make things worse if that is the issue, but it was leaking with a new washer even before I did that) 

grumpy_codger

If they aren't aligned, try unscrewing the plastic nut a little to make the plastic part lose.

And you don't need a fibre washer in this case. It has to be very elastic.

WIAWSNB

JDPower said:

Yes it can be tightened enough. Everything you said about the connection, washer, assembly etc is all correct. Yet the joint still leaks. Hence why I suspected the plastic threaded pipe to start with. Neither washer had any effect on the leak. I didn't specifically check the mating face of the pipes, I just noticed it seemed generally worn. So will take another look at that.

I will add, the pipes didn't seem quite aligned - when disconnected the brass pipe was a couple of mm below the plastic pipe, so this may have deformed the mating face of the plastic pipe (I have raised the cistern a couple of mm so they meet cleanly, which obviously would make things worse if that is the issue, but it was leaking with a new washer even before I did that) 

The rubber washer you tried - is that the same size as the fibre one? Ie, it fits neatly over the tophat, and sits on the hat rim? I'd have expected that to fill in any gouges in the plastic.

Ok, I guess one last chance with the existing fitting; undo the brass nut and examine the hat rim carefully for damage. Ditto the plastic pipe. And chance of close-up ics of both?

Then either PTFE tape or jointing compound. For the former, a couple of wraps over the tophat rim, refit the fibre washer, and tightly wrap more tape around it all, to fully cover the washer and tophat rim. You could even wrap a couple of turns around the plastic thread - wrap it clockwise, so the nut doesn't unwrap it as it screws on. Hold the copper pipe firmly to align it so as not to croass-thread the brass nut on the plastic thread (easy to do), and do it up by hand as far as possible - then tightned fully.

For the jointing compound, smear it over the tophat, fit the fibre washer, and then another smear over this. A light smear over the plastic thread. Do up as before.

Use a piece of tissue paper to get the outside bone dry, and if another drip appears, examine it closely for where - exactly - it is squeezing out from.