How to connect new Gohe tap

[Milleniumaire]

Hi,

I'm looking to replace a kitchen mono tap, which has 15mm copper tails with a Grohe mono tap and I believe this has 3/8 inch flexible tails. Details of the Gohe tap can be seen here.

The existing piping is plastic and it has some chunky connectors on the end, which I'm not familiar with. Here's a photo of the piping connected to the old (existing) tap tails:

The connector looks like it might be in three parts, but I'm not sure. I think the part that connects to the copper pipe might be some sort of push fit as the copper pipe can actually be twisted!

What is the best way to connect the 3/8" Grohe tails to plastic pipe?

Thanks.

 

[terryplumb]

Cut everything off up to the grey supply pipe and fit an isolation valve ,full bore preferably ,15 mm compression.fit into the isolation valve a 15mm to 3/8 tap tail adaptor , available from tool station ,item code 63663 , as an example. The taps flexi connects directly to it.

 

[Milleniumaire]

Thanks for the quick answer Terry.

I haven't attempted to remove the compression fitting from the plastic pipe, bit I would assume there would be a pipe insert that I would need to re-use for fitting an isolation valve to the plastic pipe? I've also read that copper olives should be used on plastic pipes, rather than brass.

Yes, I've seen the 15mm to 3/8 adaptors and suspected I might need some.

While Googling I noticed this particular Grohe tap seems to have a lot of issues, so might go for a Bristan instead as they supply everything required, including the isolation valves!

 

[terryplumb]

Yes plastic tube needs insert. You may be able to leave the nut and olive on, and connect the isolation valve to it ,if the threads are the same ( good chance as 1/2 inch bsp is common). Olives in copper or brass will be fine on plastic tube ,but you must have a pipe stiffener ( insert into pipe ). Choice of tap is entirely up to you.

 

[Milleniumaire]

Is it possible that the existing adaptors are preventing backflow? Do I need to worry about this? It will be fitted in a flat, which is in a large purpose built block of flats in a city centre. I believe there are large cold water tanks that feed all the flats. In each flat is an electric hot water cylinder. I therefore suspect that nothing is being fed directly from the mains so it is likely the pressure of both hot and cold is the same? If so, I assume I don't need to worry about backflow?

 

[terryplumb]

Cold drinking water at your kitchen tap is never from a tank ,but directly from the mains. Your pic does not show any double check valve ,but you can fit one to the cold supply . A well designed kitchen tap will not let the hot and cold mix ,keeping them apart ,until the point of discharge at the spout ,thus negating back flow. Having said that there is plenty that do not do this. If you are in a new build ,I would expect check valves to already be present ,but maybe not !

 

[Milleniumaire]

Hi, finally got my tap today, which came with 15mm tails and I purchased some full bore isolation valves (I decided no to get the Grohe). Cut off the grey pipe, containing all the existing nuts and bolts, only to find I could not push the pipe into the isolation valve - it wouldn't go due to being slightly too thick. I also tried popping some inserts I had but these just rattled around. In the end I managed to push on some plastic stop ends, but this really took some doing and I'm not convinced they are "fully" on due to the tightness of the fit. I've used these on copper and plastic pipe before and they usually push on easily, so there's something different about this particular pipe. As a result I'm at a loss how to connect anything to it. The fitting that was on the end of the plastic pipe had a built in plug that fit inside, but this was a very, very tight fit. Took me ages to get the thing off! A few photos in the hope that someone can tell me what I need to connect a 15mm isolation valve to one of these mega plastic pipes that seem to be slightly larger than 15mm.

This is part of the adaptor that was attached to the end of the pipe. Into this was screwed another fitting into which the old copper pipe tails were screwed. Unfortunately, I can't use any of the existing adaptors!

 

[oldbutnotdead]

Oh dear. Looking at the markings on that pipe it appears to say 16 x 1 (ie 16mm dia, 1mm wall thickness). This size seems to be popular for UFH systems, not common in tap runs (maybe the plumber had some in his van.....). Have a measure to confirm, then go shopping for 16-15mm adaptors

You'll (alas) have to go shopping for some inserts to fit that tube as well. The bad news- the inserts are not common between suppliers....

 

[dilalio]

Agreed. That looks like you've been left a nice problem by the original installer.
Can you trace that plastic back to something standard and replace from there with new pipe?

 

[oldbutnotdead]

Google being Google there are some answers- this https://www.jtmplumbing.co.uk/pipe-...-x-15mm-compression-transition-fitting-p20960 looks similar to what you had.

 

[Milleniumaire]

Google being Google there are some answers- this https://www.jtmplumbing.co.uk/pipe-...-x-15mm-compression-transition-fitting-p20960 looks similar to what you had.

That looks to be just the job! I assume the "shiny" end has the insert and this pushes onto the existing plastic pipe and is screwed on, just like a compression fitting. I assume, with this particular fitting I'd need to connect to a short piece of copper, then connect my isolation valve to the other end of the copper?

Alternatively, could I use something like this and would the isolation valve screw into the half inch female end? I guess it may leak as the isolation valve uses compression fittings, not those with rubber washers (like the end of the tails fitted to the tap)?

https://www.jtmplumbing.co.uk/pipe-...jtm-16mm-x-1-2-compression-female-iron-p23572

 

[oldbutnotdead]

That looks to be just the job! I assume the "shiny" end has the insert and this pushes onto the existing plastic pipe and is screwed on, just like a compression fitting. I assume, with this particular fitting I'd need to connect to a short piece of copper, then connect my isolation valve to the other end of the copper?

Alternatively, could I use something like this and would the isolation valve screw into the half inch female end? I guess it may leak as the isolation valve uses compression fittings, not those with rubber washers (like the end of the tails fitted to the tap)?

https://www.jtmplumbing.co.uk/pipe-...jtm-16mm-x-1-2-compression-female-iron-p23572

That's my take on those things, check what wall thickness their tube is (that'll tell you if the insert will fit). And yeah you can try it (I've done that bodge myself, you need a rubber washer that'll fit inside the thing for the end of the compression fitting to seal against. Or liquid PTFE or Boss White and horsehair). Have fun