Pipe Diameter Advice

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If you look at the Nene installation instructions, it shows

flow limiter, shown on page 6, don't put it in
Non return valve, item 5 page 10 try with it, then winkle it out and try again.

They're usually a white two-part plastic thing with sprung cone inside. It's probably a push fit into the metal, with an O ring on the outside. A big woodscrew will get them out, though they may be wrecked , but you don't need it with both your supplies coming from a cistern.
Often only half comes out - so be it.

I couldn't find a Tesla pdf - you may be able to.
SS, browsing these posts i haven't seen anyone ask nor have you posted whether the shower pipework is dedicated to the shower alone, i may have missed this if it is in an earlier post, so excuse me if i have, it is worth upsizing the pipework to the valve in 22mm as in the last picture because if you do fit a pump it will be required to be in 22mm in the pump manufacturers literature. hope that helps.
I'm going to have to read back over the thread, whoever said the cold was on main completely confused the matter.

It may have been me muddying the waters (!) between the bath and the shower.

The bath is on mains cold but the shower has cold from the tank and hot from the cyl.
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Chris, thank you for your in-depth replies. Greatly appreciated, as are all inputs here, guys.

I have just clambered into the loft and remeasured the tank. It is 76cm to the bottom of the tank from the plasterboard. Adding the distance from the ceiling in the bathroom below to the top of the showerhead is a metre total. So a bare minimum of 0.1 bar. Not great.

I cannot raise the tank at all. Not without removing roof tiles and timber....!

Shorky: Thanks for your comments. The cold feed comes direct off the side of the tank. The hot comes from the pipe rising into the loft but not direct from the top of the cyl., no.

I post below two pix of the pipework feeding the Triton Tesla thermostatic Mixer Valve:

First is the cold leaving near the bottom of the cold tank.


Second, the hot, tapped off the hot feed off the cyl. as it comes up through the ceiling into the loft.


Shorky, if I understand your post correctly, are you saying the 15mm stumps should be done away with? If so, I tried to persuade the plumber to do this by fitting the 22mm - 1/2" tap connectors someone (bless you, I've forgotten who!) recommended a few pages back and he gave me several bad-tempered reasons why he could not fit them. "Anyway, " he said, "It is 15mm inside the valve, so what is the point of supplying it with 22mm?"

I really seem stuck as to what to do next.
We want to stall the plumber again on the shower and get him to finish everything else. He can spend no more time after tomorrow so that will be that.

My options for rectifying the shower work at the moment seem to be either one of these or a combination, possibly of all three?:

1. Remove obstructive NRV and limiter from Tesla.

2. Re-configure the pipework for a more direct feed from the cylinder.

3. Replace the Tesla with an Aqualisa, "if it'll work on gravity, they mean it".

4. Add a pump.

Chris: I've just read my Tesla manual. There are 2 NRV's, one on each inlet. There's no talk of a flow limiter, but there is mention of a flow regulator. This, it says, is only for use on high pressure systems.
That cold take off is nowhere near the bottom of the cistern. It should be below the feed to the hot tank for a start, that's for safety reasons but would also help a bit with pressure.
Is the simple answer to my burning

"Why did the old shower work and the new one doesn't?" question,

"Because the Aqualisa was designed to work exckusively on gravity systems."?
That cold take off is nowhere near the bottom of the cistern. It should be below the feed to the hot tank for a start, that's for safety reasons but would also help a bit with pressure.

Could you elaborate, please?

I don't follow.

I mean, I understand the cold take-off is not at the bottom, but don't understand what you're saying that it should be below the hot.
If the tank runs dry while somebody is showering your setup will result in the cold supply to the shower running out first, it should be the other way around. Having the cold feed slightly lower than the feed to the hot cylinder ensures that the hot cuts out first.
OK, thanks. So, how would I alter my pipework to ensure that?
That would be close to the bottom of the tank then?

Wouldn't it pick up all the crud? Like the rotting pigeon carcasses? ;)
About an inch to an inch and a half off the bottom is ideal, which should be just below the level of the cold feed to the hot tank.
One thing - your "head"
All the manuals will say to measure the distance from the bottom of the tank, because the water level could get down there, but in practice if the inflow is fast enough then the actual level will be quite a lot higher.
So someone already HAS raised your tank. Depending on the shape, you'll have maybe half a metre more inside. :D

You found some NRVs, excellent, removing thosewill gain you maybe 0.25m! Try blowing through them - it's not all that easy, and the holes are tiny.

DOn't worry about changing the remaining 15mm pipe. The resistance is cumulative but a few inches won't make any difference. Again - remember it all goes up the same skinny 1.25 metre hose.

Hopefully any gain you get from the increased (so far) pipe size can add to the removal of NRVs and make a difference, without having to "prove" anything with your plumber.

I'd still call Triton and see if you have a Nene or one of the others.

Yeah Aqualisa stuff is pretty good, but they don't do "bar" type mixers afaik.
Silly one - make sure the gate valve(s) are wide open (then close half a turn or they'll seize).
Pipework layout, changing elbows to swept bends and all that, will hardly add you anything as the bigger resistance seems to be in the shower mixer.
If you want to prove that, unscrew the mixer (put your finger over the end!), then see what the difference in flow rate is.
ss, the last bit of pipe going into the valve reduced like that will not make a difference with a pump connected as the pressure can be the same with a pump as on mains pressure, same principles as a high pressure tap with a smaller bore, pump manufacturers like i said will require the shower pipework be piped in 22mm reduced last minute where it enters the valve, this is for adequate flow to serve the pump and it can aid in reduccing noise levels on the pump, nrv's should be fitted on hot & cold to the shower, if the hot supply is being drawn off of the vent if ive read that correctly, you may get airated water to the shower, best to be pulled off the cylinder as the first draw off or even better a surrey flange or similar.

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