I need to replaceÂ*the hot tap in my bathroom sink.Â* The bathroom is ancient, 30+ years old, and will be replaced in the next year, so I just need something simple to keep it working until then.Â* I've not fitted a new tap before, but I've done some research and have a couple of questions:

1. Assuming that the old tap is a 1/2 inch tap, do I need to buy a 1/2 inch tap, or will a modern 15m tap be OK?Â*Â*
2. From looking round on the net, a sensible option seems to be to use a flexible hose.Â* Am I right to think I should buy a 1/2 fitting for the pipe end and, depending on the answer to Q1, a half inch or 15mm fitting for the other end?3. 3. Should I use a push or compression fitting (bearing in mind I haven't done this before)?

Thanks

On Monday, 2 November 2020 09:22:00 UTC, Jedzi wrote:
I need to replaceÂ*the hot tap in my bathroom sink.Â* The bathroom is
ancient, 30+ years old

That's 1990, which would be metric (and not at all ancient in relative terms).

If it's pre-1970-something the pipework will be imperial.

1/2" pipe refers to the internal diameter, 15mm pipe is the external diameter. The same olives or solder fittings will probably fit both.

You can use a 22mm fitting with 3/4" pipe, so long as you use a 3/4" olive.
https://www.stevensonplumbing.co.uk/...-3-4-inch.html

The tap end will almost always be either 1/2" BSP or metric small-bore with a hose supplied to got to 1/2" BSP female.

To join two 1/2" BSP females (hose to hose) you need a nipple
https://www.toolstation.com/brass-hexagon-nipple/p59604


Plumbers I've used seem happy with push-fit, either JG Speedfit or Yorkshire Tectite, but I'm not sure if push-fit will work on even 3/4" imperial pipe.

To fix the new tap in the old hole you may need a
https://www.toolstation.com/split-klick-washer/p93139
or a
https://www.bes.co.uk/fix-a-tap-tap-...-orange-22022/

Owain

wrote in message
...
1/2" pipe refers to the internal diameter, 15mm pipe is the external
diameter. The same olives or solder fittings will probably fit both.

I never understood why the change from imperial to metric was accompanied by
a change in measuring internal versus external diameter of pipe. Or at
least, why imperial denoted the inside diameter of the pipe.

You never fit anything inside a copper pipe: all soldered and compression
fittings go *outside* the pipe. So it makes more sense, logically, to
measure the outside diameter of the pipe, and the inside diameter of the
solder/compression fittings into which the pipe fits (those two measurements
should be virtually the same). It explains why 1/2" copper pipe wasn't
replaced by 12 or 13 mm, but 15 mm pipe - to allow for the thickness of the
wall.

But hey, this is the imperial system we were talking about: common sense and
logic (eg using the base (10) that we are taught to count in), and having
*one* definition of a unit (instead of ounces troy, avoirdupois and
apothecaries, and instead of having UK and US pints and gallons) don't apply
to imperial. ;-)


I didn't realise that solder and compression fittings for 1/2" (nominal OD
15.9 mm) and 3/4" (nominal OD 22.2 mm) would sometimes accept 15 and 22 mm
pipe respectively. A difference of 0.9 mm for 15 mm pipe is quite a large
amount for an olive or solder joint to bridge.

My parents renovated an old cottage in the mid 1970s. I remember dad having
to take out all the old 1/2" pipe and start again because he found that he
couldn't get a water-tight seal between 1/2" pipe and 15 mm fittings, when
he needed to install additional pipe - eg when the bathroom was renovated.
After he'd done all the work, he found a specialist plumber that sold
1/2"-to-15 mm and 3/4"-to-22 mm converters (I can't remember whether they
were compression or solder) which would have allowed him to continue using
the old pipe but connect new 15 or 22 mm pipe to it.

On 02/11/2020 10:18, NY wrote:
So it makes more sense, logically, to measure the outside diameter of
the pipe..
Only for plumbers. The rest of us understand that the *purpose* of pipes
is to carry liquids and gases, and the crucial dimesion is of course the
*internal* diameter.


--
Climate Change: Socialism wearing a lab coat.

Thanks for the responses. Thinking about it, I'm probably being optimistic in saying it's only 30 years - I'd say it's more like 50+, from the hideous bright pink bath & sink.

I've measured the pipe, it's roughly 15mm externally, which doesn't tell me whether it's imperial or metric, but does tell me it's not 3/4".

Based on the responses so far:
1. It's probably not safe to assume that 15mm & 1/2" are interchangeable.
2. Given the small difference in the size though, a new 15mm tap will fit in the hole in the sink for the existing tap, even if it is 1/2".
3. Given the age, my best bet for the flexible hose is probably 1/2" pipe to 15mm tap. If I'm wrong on that, it's not a large loss (about £3 from a quick look online).

Pls shout if this doesn't make sense.

On 02/11/2020 10:41, Jedzi wrote:

Thanks for the responses. Thinking about it, I'm probably being
optimistic in saying it's only 30 years - I'd say it's more like 50+,
from the hideous bright pink bath & sink.

Ah, yes. The late 50s early sixties...then there was 'avocado'



--
Climate Change: Socialism wearing a lab coat.

On 02/11/2020 09:21, Jedzi wrote:

I need to replace the hot tap in my bathroom sink. The bathroom is
ancient, 30+ years old, and will be replaced in the next year, so I
just need something simple to keep it working until then. I've not
fitted a new tap before, but I've done some research and have a
couple of questions:

1. Assuming that the old tap is a 1/2 inch tap, do I need to buy a
1/2 inch tap, or will a modern 15m tap be OK?

Traditional taps typically have a threaded base that passes through a
hole in the basin. You pass the tap through the hole (possibly with an o
ring or washer of some sort between the tape base and the basin), and
then fix it in place with a lock nut that screws onto the threaded base.
Once fixed in place, you connect the pipes using a tap connector, which
is fitted to the end of the pipe.

e.g:

https://www.screwfix.com/p/swirl-bat...aps-pair/88965

The threaded section that sticks out the bottom of the tap will be
described as 1/2" BSP (British Standard Pipethread) or 3/4" BSP. Note
that the sizes refer to the *internal* diameter of an iron barrel (i.e.
thick walled) pipe. So the actual diameter of the thread if you measure
is is quite a bit larger than the size would suggest.

Even modern taps with threaded bases will be in one of the imperial
sizes above. Typically 1/2" on basins, and 3/4" on bath taps.

(some taps like monoblock mixers will use slim braided flexi hoses to
connect to the pipes. These *might* terminate in a 15mm compression or
push fit connector)

Tap connectors are available in compression, push fit, and solder:

https://www.screwfix.com/p/compressi...r-15mm-x/28793

https://www.screwfix.com/p/jg-speedf...r-15mm-x/12129

https://www.screwfix.com/p/endex-cop...r-15mm-x/98412

(I have shown right angled types - but straight ones are also available)

2. From looking round
on the net, a sensible option seems to be to use a flexible hose. Am
I right to think I should buy a 1/2 fitting for the pipe end and,
depending on the answer to Q1, a half inch or 15mm fitting for the
other end?3.

The easiest swap would be "like for like" - assuming the tap projects a
similar distance below the basin, you will likely find you can simply
reuse the existing tap connector. Especially of there is a bit of "give"
in the pipe to allow it to be reposisitioned a bit.

If you can't get the new tap to match up with the existing tap
connector, then yes you could use a flexi connector.

3. Should I use a push or compression fitting (bearing
in mind I haven't done this before)?

In the circumstances, I would go for push fit. Something like:

https://www.screwfix.com/p/jg-speedf...m-2-pack/9938g

The 1/2" BSP connector would screw onto the tap (with a fibre washer to
make the seal). The push fit end just pushes onto the cut end of a pipe.

Note that you will need to use a pipe slice to cut the pipe and not a
hacksaw since the internal rubber seals in a push fit fitting need a
slightly tapered pipe end and no sharp bits, and that is difficult to do
with a hacksaw. Something like:

https://www.screwfix.com/p/3-28mm-ma...e-cutter/49428

will do the job. Put round the pipe, and tighten the thumb wheel, spin
it round the pipe a couple of times, and tighten again. Rinse and repeat
until the pipe is cut.

Or you can get "automatic" versions like:;

https://www.screwfix.com/p/monument-...e-cutter/29457

Just push onto the pipe and rotate in the indicated direction until the
cut is done.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 02/11/2020 10:50, The Natural Philosopher wrote:
On 02/11/2020 10:41, Jedzi wrote:

Thanks for the responses.Â* Thinking about it, I'm probably being
optimistic in saying it's only 30 years - I'd say it's more like 50+,
from the hideous bright pink bath & sink.

Ah, yes. The late 50s early sixties...then there was 'avocado'




I noticed the latest fashion is for coloured plastic window frames.

I can't help but wonder if in 20 years time they will be the avocado bath.

In article ,
Jedzi wrote:
Thanks for the responses. Thinking about it, I'm probably being
optimistic in saying it's only 30 years - I'd say it's more like 50+,
from the hideous bright pink bath & sink.

I've measured the pipe, it's roughly 15mm externally, which doesn't tell
me whether it's imperial or metric, but does tell me it's not 3/4".

15mm tube is near enough 15mm measured with digital callipers. 1/2" is
nearer 16mm (15.88) (external diameter)

But that is irrelevant as regards a tap connector. There's a very good
chance a new tap will have the same thread as the old, and not require any
alteration to the pipework.

--
*Oh, what a tangled website we weave when first we practice *

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 2 Nov 2020 01:21:56 -0800 (PST), Jedzi wrote:

I need to replaceÂ*the hot tap in my bathroom sink.

Why? Leaking gland? Unless that shaft is very worn and tightening the
gland nut and/or repacking the gland might suffice. Dripping, replace
the washer, if the seat isn't cracked.

Mind you getting the cover and/or top of the tap off to do that on a
30+ year old tap could be fun and replacing the whole thing the
"easy" option.

1. Assuming that the old tap is a 1/2 inch tap, do I need to buy a 1/2
inch tap, or will a modern 15m tap be OK?

A modern tap will still be 1/2" BSP for the tap connector.

2. From looking round on the net, a sensible option seems to be to use a flexible hose.

As others have said you might be lucky and the new tap will have a
stem close enough in length to the old to allow it to connect to the
existing pipe work.

Flexible hoses are OK 1/2" BSP tap connector one end (and new fibre
wsher) and the other end I'd go for 15 mm compression.

Due to the existing pipe possibly being 1/2" I wouldn't like to say a
pushfit would work or be reliable. 1/2" is I *think* slightly smaller
in OD that than 15 mm.

1/2" ID. Wall thickness 0.040" x 2 = 0.58" OD = 14.723 mm ie 0.277 mm
or 11 thou overall, murdering up a 15 mm fitting with 15 mm olive
should take that up no problem.

Be aware that a lot of references on the web to 1/2" copper tube
dimensions are for the US not UK...

3/4" pipe and 22 mm compression with 22 mm olive do NOT, BTDTGTTS.
You can get 3/4" olives for 22 mm fittings that does work. 1/2" to 15
mm olives aren't available....

Am I right to think I should buy a 1/2 fitting for the pipe end and,
depending on the answer to Q1, a half inch or 15mm fitting for the other
end?

You will be hard pushed to find a 1/2" pipe end or 15 mm tap end. Try
the otherway round. B-)

3. Should I use a push or compression fitting (bearing in mind I haven't
done this before)?

See above. Push fit are designmed to work on 15 mm OD pipe. If you
have 1/2" pipe (14.723 mm OD) I suspect that might be outside the
range acceptable for push fit. Compresssion can just be murdered up.
B-) You will need two decent spanners for compression.

Oh and probably a basin wrench to get at the back nut to remove the
old tap and fit the new one.

--
Cheers
Dave.

In message
Jedzi wrote:


I need to replace*the hot tap in my bathroom sink.* The bathroom is
ancient, 30+ years old, and will be replaced in the next year, so I just
need something simple to keep it working until then.* I've not fitted a
new tap before, but I've done some research and have a couple of
questions:

1. Assuming that the old tap is a 1/2 inch tap, do I need to buy a 1/2
inch tap, or will a modern 15m tap be OK?**
2. From looking round on the net, a sensible option seems to be to use a
flexible hose.* Am I right to think I should buy a 1/2 fitting for the
pipe end and, depending on the answer to Q1, a half inch or 15mm fitting
for the other end?3. 3. Should I use a push or compression fitting
(bearing in mind I haven't done this before)?

Thanks

Connecting your new tap into the existing plumbing may be the least of
your worries....
Removing the old tap after such a long time may well be problematical as
the lock nut will be not only difficult to access but may be seized on.
Think about how you might cut the locknut off or the tap top itself.

I am speaking from experience as I wanted to change the cold tap washer
but broke the sink and ended up changing the sink, taps and drain for my
trouble.

Good luck

John


--
John Bryan

Thanks for all of the responses - much appreciated and gives me a lot more confidence to tackle the job. I hadn't appreciate that new taps are still sold in imperial.

In terms of getting the old tap off, I can see that is very likely to be a problem. Tricks I'm aware of: penetrating oil, light tap with a hammer, heat, Please let me know if there's anything else.

One quick question on that: am I likely to be better off with a fixed or adjustable basin wrench?

On 2 Nov 2020 at 23:07:10 GMT, "Jedzi" wrote:


Thanks for all of the responses - much appreciated and gives me a lot more
confidence to tackle the job. I hadn't appreciate that new taps are still
sold in imperial.

In terms of getting the old tap off, I can see that is very likely to be a
problem. Tricks I'm aware of: penetrating oil, light tap with a hammer,
heat, Please let me know if there's anything else.

One quick question on that: am I likely to be better off with a fixed or
adjustable basin wrench?

I think this kind is more likely to enable access:


https://www.screwfix.com/p/basin-wrench-1-/14631

But it is well worth getting one of this kind:

https://www.screwfix.com/p/basin-wrench/13294

if you don't have one. Partly because it may work better with your particular
tap and partly because it can be quite good for stopping things turning such
as taps or the fixed part of fittings you are trying to undo.

--
Roger Hayter

On 02/11/2020 10:41, Jedzi wrote:

Thanks for the responses. Thinking about it, I'm probably being
optimistic in saying it's only 30 years - I'd say it's more like 50+,
from the hideous bright pink bath & sink.

I've measured the pipe, it's roughly 15mm externally, which doesn't
tell me whether it's imperial or metric, but does tell me it's not
3/4".

Based on the responses so far:

1. It's probably not safe to assume that 15mm & 1/2" are
interchangeable.

A 15mm compression fitting will usually fit both... however

2. Given the small difference in the size though, a new 15mm tap will
fit in the hole in the sink for the existing tap, even if it is
1/2".

Probably no such thing as a 15mm tap. Even a new basin tap will have a
1/2" BSP thread.

3. Given the age, my best bet for the flexible hose is probably 1/2"
pipe to 15mm tap. If I'm wrong on that, it's not a large loss (about
£3 from a quick look online).

Your best bet is swap the tap and reuse the existing tap connector
without any pipework changes at all.

Pls shout if this doesn't make sense.

SEE ABOVE ;-)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 02/11/2020 23:07, Jedzi wrote:

Thanks for all of the responses - much appreciated and gives me a lot more confidence to tackle the job. I hadn't appreciate that new taps are still sold in imperial.

In terms of getting the old tap off, I can see that is very likely to be a problem. Tricks I'm aware of: penetrating oil, light tap with a hammer, heat, Please let me know if there's anything else.

One quick question on that: am I likely to be better off with a fixed or adjustable basin wrench?

Given the price of them, buy one of each to be on the safe side...

Often I find the backnut on the tap easier with the fixed type, and tap
connector on the pipe easier with the automatic type.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 2 Nov 2020 23:49:35 GMT, Roger Hayter wrote:

In terms of getting the old tap off, I can see that is very likely
to
be a problem. Tricks I'm aware of: penetrating oil, light tap
with a
hammer, heat, Please let me know if there's anything else.

Depening on what was used to seal the tap to basin penetrating oil
might not have much effect on 30+ year old plumbers mait. It'll be
set hard and solid. Remember the basin in porcelain, it can crack, be
very gentle tapping the tap. The hole in the basin won't be perfectly
round, if the plumbers mait is in the void between tap stem and sides
of hole you could be trying to force round something that wants a
bigger hole to rotate.

Heat, I wouldn't. OK the basin has been fired but that would have
heated and cooled the whole thing fairly evenly, not sure how the
glaze would take to being spot heated.

One quick question on that: am I likely to be better off with a
fixed
or adjustable basin wrench?

I think this kind is more likely to enable access:

https://www.screwfix.com/p/basin-wrench-1-/14631

I find with adjustable almost anything is that they have a habit of
adjusting themselves looser as your fiddling about gettting them onto
what ever. Or loosen if you don't keep the pressure on them that is
holding the setting.

But it is well worth getting one of this kind:

https://www.screwfix.com/p/basin-wrench/13294

Having said the above the tolerance on these fixed type basin
wrenches leaves a little to be desired. Generally they are a loose
fit to the back nuts but at least once fitted and held up don't "self
adjust" and when rotated will grip the back nut.You can also clamp
mole grips or similar to the shaft to provide a good hand grip or
something gently tap.

--
Cheers
Dave.

"NY" wrote in :


I never understood why the change from imperial to metric was
accompanied by a change in measuring internal versus external diameter
of pipe. Or at least, why imperial denoted the inside diameter of the
pipe.


Old school emphasis was on the carrying capacity of the pipe/tube whether
it be lead, copper or iron, the inner dia, new age thinking is the
compatibility of the fittings, the outside dia. We now have multiple 15mm
pipes/tubes in materials with different carrying capacities, plastic with
thickers walls and restrictions of internal stiffeners at joints will not
carry the same volumes for a given pressure drop as copper.


I didn't realise that solder and compression fittings for 1/2"
(nominal OD 15.9 mm) and 3/4" (nominal OD 22.2 mm) would sometimes
accept 15 and 22 mm pipe respectively. A difference of 0.9 mm for 15
mm pipe is quite a large amount for an olive or solder joint to
bridge.


Your imperial pipe dims don't seem right, an imperial 3/4" olive is
thicker than a 22mm olive to compensate for the _smaller_ o/d of a 3/4"
pipe.

A quick search shows:

3/4" imperial, 0.846" o/d == 21.49mm, too much diff for a 22mm olive
hence the availability of 3/4" olives but perhaps ok on 22mm solder but
prob only on end feed with extra solder.

1/2" imperial, 0.596" o/d == 15.14 mm so basically compatible with 15mm
fittings, this is readily accepted as the case

On 4 Nov 2020 at 20:42:39 GMT, "Peter Burke" wrote:

"NY" wrote in :


I never understood why the change from imperial to metric was
accompanied by a change in measuring internal versus external diameter
of pipe. Or at least, why imperial denoted the inside diameter of the
pipe.


Old school emphasis was on the carrying capacity of the pipe/tube whether
it be lead, copper or iron, the inner dia, new age thinking is the
compatibility of the fittings, the outside dia. We now have multiple 15mm
pipes/tubes in materials with different carrying capacities, plastic with
thickers walls and restrictions of internal stiffeners at joints will not
carry the same volumes for a given pressure drop as copper.


I didn't realise that solder and compression fittings for 1/2"
(nominal OD 15.9 mm) and 3/4" (nominal OD 22.2 mm) would sometimes
accept 15 and 22 mm pipe respectively. A difference of 0.9 mm for 15
mm pipe is quite a large amount for an olive or solder joint to
bridge.


Your imperial pipe dims don't seem right, an imperial 3/4" olive is
thicker than a 22mm olive to compensate for the _smaller_ o/d of a 3/4"
pipe.

A quick search shows:

3/4" imperial, 0.846" o/d == 21.49mm, too much diff for a 22mm olive
hence the availability of 3/4" olives but perhaps ok on 22mm solder but
prob only on end feed with extra solder.

1/2" imperial, 0.596" o/d == 15.14 mm so basically compatible with 15mm
fittings, this is readily accepted as the case

IME it took a *lot* of work with steel wool on 15mm end feed fittings to get
the 1/2" pipe to go in at all. (Only applicable at the weekend when convertor
ones weren't handy.)
--
Roger Hayter

On Monday, November 2, 2020 at 12:36:47 PM UTC, Dave Liquorice wrote:

I need to replace the hot tap in my bathroom sink.

Why? Leaking gland? Unless that shaft is very worn and tightening the gland nut and/or repacking the gland might suffice. Dripping, replace the washer, if the seat isn't cracked.

The basic problem is that the very, very old plastic head just turns on the valve, so either the valve or the head has lost it's thread. Ive been to my local plumbers merchant. They told me that you cant get this type of valve anymore, photo he https://bit.ly/3n2Rdw9

I messaged an online plumbing store and they recommended a conversion kit: https://bit.ly/366v5Kk Unfortunately it came with no instructions and I can't find anything useful on the web. I've spent ages looking at it, but can't see how to fit it. https://shorturl.at/hDMX8

So I'd given up on these attempts and decided to try and change the whole tap. I'd be very happy to be told I've missed something and there's a much easier way.

Jedzi

On Saturday, 7 November 2020 12:51:49 UTC, Jedzi wrote:
I messaged an online plumbing store and they recommended a conversion
kit: https://bit.ly/366v5Kk Unfortunately it came with no instructions
and I can't find anything useful on the web. I've spent ages looking
at it, but can't see how to fit it. https://shorturl.at/hDMX8

Also called a tap reviver.

Video at
https://www.youtube.com/watch?v=Xvik57gmEDI

Basically, *turn off the water*, take the old handle off, unscrew the tap innards from the tap, and screw in the new innards. Put the new head on top.

Owain

On Sat, 7 Nov 2020 04:51:46 -0800 (PST), Jedzi wrote:

The basic problem is that the very, very old plastic head just turns on
the valve, so either the valve or the head has lost it's thread.

Normally splines rather than screw on, though there will be screw
under a cover to hold the handle on.

I've been to my local plumbers merchant. They told me that you can't
get this type of valve anymore, photo he https://bit.ly/3n2Rdw9

Splines look a bit knackered but a new handle ought to fit and the
possibly bad assumption that they haven't changed the number of
"standard" splines theer are over the years...

I messaged an online plumbing store and they recommended a conversion
kit: https://bit.ly/366v5Kk Unfortunately it came with no instructions
and I can't find anything useful on the web. I've spent ages looking at
it, but can't see how to fit it. https://shorturl.at/hDMX8

That's a composite kit with various collars and washers to enable the
valve body fit 1/2" of 3/4" taps. At aguess you'll need the right
hand collar and the smaller conical washer. You may need to remove
the flat washer to fit the conical one. Not sure what open top hat
things are for. Fiddle about and see where they fit?

--
Cheers
Dave.

On Saturday, November 7, 2020 at 8:35:52 PM UTC, Dave Liquorice wrote:

Normally splines rather than screw on, though there will be screw under a cover to hold the handle on.
Sorry, poor explanation on my part €“ the plastic tap head pushes on (no screw). I was referring to the €˜thread inside the plastic tap head that the splines fit into, which is now worn.

Splines look a bit knackered but a new handle ought to fit and the possibly bad assumption that they haven't changed the number of "standard" splines theer are over the years...
Ive tried swopping the cold and hot around. The €˜good plastic tap head from the cold works on this hot top, which suggests the valve & splines while ancient, still work.

Ive also tried swapping a valve in from another sink and that works.

That's a composite kit with various collars and washers to enable the valve body fit 1/2" of 3/4" taps. At aguess you'll need the right hand collar and the smaller conical washer. You may need to remove the flat washer to fit the conical one. Not sure what open top hat things are for. Fiddle about and see where they fit?
The 2nd from the left on the middle row works to allow me to screw the valve in to the tap itself.

The problem I then have is that the new valve is too short to turn the flow off. Im pretty sure it needs one of the two fittings on the left of the front row, which I assume fit over the bottom of the valve. The problem is that theyre a hard plastic and I cant get them on. Ive tried warming them in water, but no joy.

On 8 Nov 2020 at 10:20:49 GMT, "Jedzi" wrote:

On Saturday, November 7, 2020 at 8:35:52 PM UTC, Dave Liquorice wrote:

Normally splines rather than screw on, though there will be screw under a
cover to hold the handle on.
Sorry, poor explanation on my part €“ the plastic tap head pushes on (no
screw). I was referring to the €˜thread inside the plastic tap head that the
splines fit into, which is now worn.

Splines look a bit knackered but a new handle ought to fit and the possibly
bad assumption that they haven't changed the number of "standard" splines
theer are over the years...
Ive tried swopping the cold and hot around. The €˜good plastic tap head
from the cold works on this hot top, which suggests the valve & splines while
ancient, still work.

Ive also tried swapping a valve in from another sink and that works.

That's a composite kit with various collars and washers to enable the valve
body fit 1/2" of 3/4" taps. At aguess you'll need the right hand collar and
the smaller conical washer. You may need to remove the flat washer to fit
the conical one. Not sure what open top hat things are for. Fiddle about and
see where they fit?
The 2nd from the left on the middle row works to allow me to screw the valve
in to the tap itself.

The problem I then have is that the new valve is too short to turn the flow
off. Im pretty sure it needs one of the two fittings on the left of the
front row, which I assume fit over the bottom of the valve. The problem is
that theyre a hard plastic and I cant get them on. Ive tried warming them
in water, but no joy.

Possibly the hard plastic bits are supposed to fit in the valve seat inside
the tap to raise/narrow it so the new washer will fit?

--
Roger Hayter