Pressure relief pipework

Went to a job today and noticed the blow off pipe was copper from boiler then plastic then copper to outside.

I know that it has to be copper for unvented hot water stores but what about combis?

Normally it would have to be metal throughout, but some C&M Britony boilers were supplied with a short length (300mm) of clear plastic tube which was supposed to be used to link the PRV outlet pipe to the rest of the discharge pipework. Was it a Britony boiler?

no, Worcester CDi (or something, it was less than 12months old anyway).

I've always thought it had to be copper but is that in a reg somewhere ChrisH? There won't be any pressure on the open-ended pipe so I can't see why plastic isn't OK. Likely to be within the one or two metre radius from the boiler, but hey.

Coincidentally I hear Baxi are advising that the pipe from a boiler to an open vent should "preferably" be copper. Also, has anyone noticed the description which is with Pulsar's plastic pipes; one type is for H & C water and the other for Vented CH systems.
The penny may be dropping that it isn't acceptable to use a pipe which may burst before the PRV lets go.
As mentioned before, Polypipe said they get a complaint every week that a sealed system has burst a plastic pipe.

ChrisR said:

is that in a reg somewhere ChrisH?

Click to expand...

I can't think of one off-hand, other than MIs, but since the PRV discharge could possibly be steam the pipework ought to be able to withstand 100°C for a reasonable time, which I doubt that plastic would.

When I started fitting combis (early Vaillants) I didn't even realise that they needed PRV discharge pipework (nothing about it in the MIs - I suppose the krauts assumed that we'd be proper Meisters who'd know about these things!) and I just left them to discharge wherever.