Boiler Pressure Relief Valve discharge pipe - copper vs plastic

LittleJoe · 12 May 2021

Hi,
I'm currently helping my son renovate his first house and the house had a new boiler a few years ago and was fitted with a Condensing Boiler, Potterton Performa 24 ECO HE. The plastic Condensate discharge pipe and the 15mm copper pressure relief valve discharge pipe have been run out of the boiler cupboard and along the skirting boards through two bedrooms and out of the wall. The pipes are exposed to view and look a mess.
As I am doing some work in the ceiling avoid above the kitchen which is also below the boiler cupboard, I thought I would take the opportunity to re-run the pipes through the ceiling void and out of the kitchen wall.
The pipes will need to run through 6 joists. The boiler installation manual states that the pressure relief valve discharge pipe should be 15mm copper. It would make the job a lot easier for me if I was able to use 15mm plastic barrier pipe (Hep20, JG Speedfit) instead of the copper so that it will be easier to feed the pipe through the holes in the joists. Would there be any reason or problem in using 15mm plastic barrier piping?
The first metre or so of pipe from the boiler I could use 15mm copper and then use plastic barrier pipe for the rest of the run.
Any advice aprreciated.
Thanks.

muggles · 12 May 2021

You'd need to ensure that the pipe was suitably temperature rated for the application. Be aware that you're only supposed to drill holes in joists in a zone between 25% and 40% of the total span

LittleJoe · 12 May 2021

Thanks Muggles. I'll try and establish the temperature rating of the 15mm Hep20 barrier pipe. I know it is suitable for central heating so I would have thought it should be OK for a pressure relief valve discharge pipe.

footprints · 12 May 2021

If the maker specifies copper then stick with it.

MJN · 12 May 2021

LittleJoe said:
Thanks Muggles. I'll try and establish the temperature rating of the 15mm Hep20 barrier pipe. I know it is suitable for central heating so I would have thought it should be OK for a pressure relief valve discharge pipe.

Bear in mind, however, that the pipe's usage would be in a fault condition which could be 110°C (I think that's the upper limit for overheat detection/restriction) at 3 bar i.e. superheated steam. You need to be confident the pipe can maintain its form and purpose for that worst-case scenario.

oldbutnotdead · 12 May 2021

I believe (though please check this yourself) that Hep2O barrier pipe is rated for a limited number of overheat incidents (it is the only barrier pipe I know of which is allowed anywhere on solid fuel systems).
That being said, every time the thing is serviced or (worse) CP12 inspected you'll have a fault recorded. Stick with copper, remember it has to run downhill

ianmcd · 13 May 2021

a PRV discharge does not have to be barrier pipe, if you are using PEX it will have to be rated temp wise for the PRV discharge standard pipe is not, but you can get stuff that is, some manus now use a combined Condensate and PRV discharge on standard pipe but they specify that so over rides other instructions, personally I dont see a problem with what you plan, but your house insurer may feel different if something happened , in the event of a genuine discharge at 3 Bar and extremely high temperatures you are looking at pressurised steam and not CH temp water as you assume , very rare, but that is why the safety device is there in the first place

Mr.B · 23 Feb 2024

Quick question.

All the above noted and assuming 15mm copper was used from the PRV to ground floor outside, is there a maximum run length and/or maximum number of elbows like there is with unvented G2 situations? I can't see a reference to either. (does the 15mm copper have to be insulated along its length in the garage?)

I can see the run has to be contnuously downhill but, again, I can't see a reference to the degree of downhill. I ask coz in my situation two and a half metres of the run would be clipped to the wall just above a worktop in the garage and the run wouldn't have a massive fall (still running downhill but not by a vast amount) before it drops down nicely to low level and out through the exterior wall (6" above ground level and pointing down).

As it happens it's occurring to me as I write that it would run immediately below the 40mm condensate (which I realise DOES have a recommended fall) so maybe I've answered my own question ... the 15mm copper would run parallel with the condensate and would, therefore, have a respectable enough fall on it.

In his recent quote the proposed installer has referred to providing the Expansion Vessel but hasn't mentioned providing the PRV or its pipework and will have just assumed it'll be done without specifically mentioning it, which is OK but I like to know what's what beforehand and be sure the run is feasible, practical (and permitted) in the garage.

I just measured the total length of the run for both the condensate and the PRV discharge pipe and it's a shade over four metres.

A pity you can't run the PRV discharge in the same pipe as the condensate but I can see the logic of not being able to do so.

Ta.

DP · 23 Feb 2024

MJN said:
Bear in mind, however, that the pipe's usage would be in a fault condition which could be 110°C (I think that's the upper limit for overheat detection/restriction) at 3 bar i.e. superheated steam. You need to be confident the pipe can maintain its form and purpose for that worst-case scenario.

And, plastic pipe will not withstand that temperature
Many years ago an installer posted an incidence where a boiler overheated and plastic pipe “unzipped” due to high temperature

Mr.B · 23 Feb 2024

No dispute in what you say there, no plastic planned for the PRV discharge, but any thoughts regarding my query about any possible limits re. length of the run and elbows?

Mr.B · 24 Feb 2024

Mr.B said:
Quick question.

All the above noted and assuming 15mm copper was used from the PRV to ground floor outside, is there a maximum run length and/or maximum number of elbows like there is with unvented G2 situations? I can't see a reference to either. (does the 15mm copper have to be insulated along its length in the garage?)

I can see the run has to be contnuously downhill but, again, I can't see a reference to the degree of downhill. I ask coz in my situation two and a half metres of the run would be clipped to the wall just above a worktop in the garage and the run wouldn't have a massive fall (still running downhill but not by a vast amount) before it drops down nicely to low level and out through the exterior wall (6" above ground level and pointing down).

As it happens it's occurring to me as I write that it would run immediately below the 40mm condensate (which I realise DOES have a recommended fall) so maybe I've answered my own question ... the 15mm copper would run parallel with the condensate and would, therefore, have a respectable enough fall on it.

In his recent quote the proposed installer has referred to providing the Expansion Vessel but hasn't mentioned providing the PRV or its pipework and will have just assumed it'll be done without specifically mentioning it, which is OK but I like to know what's what beforehand and be sure the run is feasible, practical (and permitted) in the garage.

I just measured the total length of the run for both the condensate and the PRV discharge pipe and it's a shade over four metres.

A pity you can't run the PRV discharge in the same pipe as the condensate but I can see the logic of not being able to do so.

Ta.

denso13 · 24 Feb 2024

Mr.B said:
My query (above ) might have got lost amid the other replies

Which is one reason it is against the rules to resurrect old threads. Better off with a new one.

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Boiler Pressure Relief Valve discharge pipe - copper vs plastic

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