Boiler PRV outflow pipe

Dec 05, 2023 Last reply: 2 years ago 5 Replies
T

I may have mentioned this before but our CH boiler is situated in the bathroom airing cupboard on an internal wall with the flue coming out the top and through the roof. Currently the Pressure Relief Valve outflow just disappears under the floor and vents into the floor space. This has not been a problem so far with the only venting occurring when I accidentally over pressurised the system.



I believe that it is a requirement now to be able to see if the PRV is venting. Short of creating a convoluted route lifting floor boards to get it outside which is not going to happen. To avoid freezing issues I have re-routed the condensate pipe so that it runs through a running trap before it connects to the stack which again is internal. My question is can I also vent the PRV outflow into the 40mm section of the condensate pipe which runs just below the PRV pipe which to me seems the logical thing to do?



Just asking in case there are any gotchas.



Richard


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T

You REALLY don't want your presssure relief valve venting into your floor space. Your expansion vessel or PRV will cause leaks at some point in the future.

A tun dish in the pipework is the normal way of making any leakage visible. Can't see why it can't drain into your condensate drain though.

Tim

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J

Depending on the circumstances this solution seems to be somewhere between "unusual" and "down right daft" :-)

Suspended Ground floor into a floor void, over soil etc, perhaps. First floor onto lounge ceiling, less good.

You can, although their are rules about the way you do it. You will need a tundish made from suitable material to withstand the heat, and prevent user contact. WB have a Technical Bulletin on it:

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T

Glad I asked. The building is a bungalow and the PRV is discharging under a suspended wooden floor onto concrete.

I read the WB technical bulletin and some other info about on the web but I cannot find a definitive answer to my specific situation. If as planned I used a Tundish discharging into a 40mm waste pipe would the waste pipe be able to withstand temperatures of up to 75degC?

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N

Are you sure the pipe just terminates under the suspended floor, rather than going out through a wall and terminating over a drain? If so, find whoever did it and ask them why they thought that was acceptable.

75C is pushing it for plastic waste pipe, and I'm not convinced that a tundish is a wonderful idea. I would simply extend the existing pipe so that it goes through an outside wall, add a couple of elbows to turn it back on itself. It will then be obvious if the PRV is weeping and water can't spray out on an unsuspecting passer-by.
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J

ok, so unlikely to cause significant damage, but not much in the way of a visible warning. The system losing pressure however would be an indirect one.

The short answer is "yes". It would be on the limit for a long term temperature for PVC for example, but for a short term not a problem.

(and chances are your pipe is probably not PVC since push fit waste pipe is normally Polypropylene, and solvent weld normally ABS)

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