Pressure relief valve termination

[diamondgas]

Okay peeps ... this seems a good section of the forum, away from 'Joe Bloggs' to explore the grey areas of our profession :shades_smile:

Prompted by a few posts on the forum regarding regulations about where the Combi Boiler prv 'must' and 'can' be terminated, and concerns regarding it!

• Outside
• inside
• visible
• none visible

I thought it appropriate to discuss termination ..... Please share your experience and advice. Considering the forum is "Gas Safe Forum" please where possible back it up with gas Safe TB or Internet reference for future readers ... I think it important to have this sort of debate in hope to dispel concerns about the seriousness of some of the issues we encounter..

Cheers!

Bye-the-way. Don't think I know the answer coz I am waiting to see what comes!

 

[SimonJohns]

I can see the only argument for this being that there is not a plastic pipe rated to 100*c so that wouldn't be able to take the discharge from the boiler in the event of a failure of the boiler for any reason. But training centres can do this for ease of installation and because their "exempt" from the regs as to give candidates a good fault finding experience


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[GQuigley67]

but you can have discharges from unvented going into plastic which would be 100+ degrees

 

[SimonJohns]

but you can have discharges from unvented going into plastic which would be 100+ degrees

How can it get above 100 in a unvented. The tpv will blow at 95

The boiler could be any temp. The only condition is above 3bar


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[desrob]

i phoned gas safe and the boilers manufactures and they both say plastic is unacceptable, it must be metalic pipe to outside and turning back into the wall for safety reasons.

 

[diamondgas]

i phoned gas safe and the boilers manufactures and they both say plastic is unacceptable, it must be metalic pipe to outside and turning back into the wall for safety reasons.

I don't dispute what you've been told desrob, however there are situations where termination outside may be extremly difficult if not impossible. Hi rise flats come to mind, center of the house or in a cellar ... If you have a soil pipe or drain near by and can use suitable materials, why can't it be an alternative, if unorthadox, option?

 

[mfgs]

I'm sure I was told before, after a certain length of pipe then you can convert to plastic. Cant for the life of me remember the measurement and not sure if its even correct, anyone else heard this? Reasoning was that it would have time to cool down before hitting the plastic pipe.

 

[diamondgas]

Maybe manufacturers should start fitting TPRV's rather than PRV's? Is it also true that the PRV pipe should not rise from the boiler? I'm positive I've seen then fitted up and over loft spaces B4!

A story regards external termination that bothered me. Attended a job where an exp vessel had 'exploded'! Turned out it had lost it's charge and was passing slightly. Custard kept topping up! Eventually the pipe froze solid and the pressure built up and blew apart the exp vessel! 😀

Now i know it needs to be temp proof and discharge in a place where no person can be scalded. It also needs to be visible! Now a tundish can be used with UV Cylinders but not PRV's is that because it's more possible for the discharge to be steam from a combi?

 

[AWheating]

have seen plenty of prv connected to internal waste systems from combis etc.... and i have fitted many discharges from unvented cylinders to waste systems also. I dont know if its different for just a prv from a boiler but for unvented you have to gain permission from local building control in writing before you can connect to a waste, and of course do it correctly using a hepvo valve and push fit waste rated for high temps.