PEX composite pipes

I am slowly seeing the advantages of this type of piping.
However I am aware that plumbers do not connect the hot water piping close to the hot geyser outlets. Instead they use copper piping for a short distance before connecting the PEX pipe.
I’m having leaking problems with a 22mm PEX fitting (for a heat pump) at the hot outlet of the geyser.

The main advantage of this kind of pipe is the price. Absolutely absolutely the price. Copper is just insanely expensive now. And then you get the thin stuff that corrode through in a few years too. Nope. Never again. PEX whenever I can.

But! We have a problem.
It’s not the pipe itself but the fittings. Our fittings (inserts) are plastic. Overseas they are stainless steel so wrt hot water we have a problem!

Shop better. :slight_smile:

They are out in the market, the metal fittings.

Where? I can’t find them anywhere…

Why not get a mechanical mixer that mix in cold water with the geyser outlet, to drop it down to 55 degrees celsius. The very reason for this, is to let your pex and that plastic fitting last longer. This is especially needed if you have a solar geyser where the temps go much higher than even 75 degrees.

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Not really. The fitting is subject to the geyser temperature not only when you are using hot water.
Those mixers are to reduce the danger of very hot water by users.

see if this helps

(or your preferred plumbing supply shop)


You said it!

Adding a tempering valve is a legal requirement if you have a solar hot water system. The temperature coming out of the faucet may not be more than 55°C.


Question though. Those plastic inserts for the PEX piping… can they handle 55°C? I believe that’s probably the deciding factor in this mini-debate. If they can, then the answer is easy. A tempering valve, and a length of copper piping for the first meter or so, and then you can run PEX from there.

If not, you probably need the stainless inserts.

geyser → copper → tempering valve → some more copper if you think → copper coupler → pex

I dont have perfect evidence, but I found a part in the wall, close to the kitchen, that was patched before I moved in to this house. Copper → pex → copper. It has never had an issue…until I drilled into the pex without knowing it was there. It seemed old too by at least a few years before I opened the wall up. From that experience I think its ok, as long as the temp is dropped to 55 at the geyser outlet.

Something tells me the reason the PEX is there, is because someone else drilled into the copper.

International plumbing specs seem to have a number around 80°C for “PEX”.

Local brand Cobra specify 70°C for their MLP PEX system (so, should include the inserts). One older catalogue actually included the following:

MLP pipe is not designed to be used on solar installations upstream of a tempering valve.

Something I did come across on the web (plumbers giving advice) and various catalogues, is to make sure to use pipe, inserts, etc from the same brand and then to also make sure that it is from the same system - there is more than one type of “PEX”, and even if pipe diameters etc. are identical PEX-A inserts might not work on PEX-B.

EDIT: SANS 10252 (Water supply and drainage for buildings) also specifies:

Any plastic piping systems for hot water use shall be class 2 (70 °C operating temperature), and shall have a minimum operating pressure (M.O.P) of 600 kPa (6 bar) at 70 °C.

So, if SABS marked and indicated as suitable for domestic hot water, then temps up to maximum 70°C should be okay.

Cobra MLP pipe spec (note they also had a single layer product as opposed to this Multi-Layer)


Other common brand that seems generally available in ZA , specifically relating to inserts:

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I was thinking the exact same thing! Pipe is in the stupidest place of a wall you can image. At least now I know it is there.

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@Richard_Mackay does your GeyserWise map/replace to that heatpump controller underneath it? I also have the bottom one and would love to upgrade it to something I can link in Node Red on my network or control with a ESP but could not find any detail on the unit.

No. They are independent.
The newer ITS heat pump has Wi-Fi however: 4.5kW Super ITS Residential Heat Pump
If you were really keen maybe you can replace the control PCB like we do with the Geyserwise systems…
I’m sure a lot of these heat pumps are identical with the outlets name on them (for which they pay)

@_a_a_a Please provide the official decree itr.
I posted this on another forum and it was challenged…

From SANS 10252-1 2012:


(I just googled the terms until I found the answer I was looking for without reading any further, which is definitely not good science/research. But this should give you a good starting point to “do your own research”.)

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