Boiler plumbing

[Bodgit]

In the next year or so I would like to get a new condensing boiler and put it into the loft. As I have the bathroom in pieces at the moment I've taken the opportunity to get a gas feed plumbed into the loft in preparation. I'd also like to plumb in the condensate drain and pressure relief valve outlet but have a couple of questions:

- The toilet overflow is made from 3/4" copper pipe. Can I tee into this for the pressure relief valve, downstream of the toilet or should I drill a separate hole in the wall? The latter would be a pain!

- What's the normal way to connect the condensate drain? I believe you're supposed to use plastic pipe of no less than 22mm. Is it usual to use plastic overflow pipe for this (this is slightly less than

22mm), or 22mm plastic pipe? If it's the latter, what fitting do you use to connect this to a 40mm waste pipe or soil stack? I assume I'll need a trap. Are there are 22mm ones? Is it unusual for the trap to be in the loft? - as it would be easier to access it there.

Any advice gratefully received. Dave.

[Tony Bryer]

Plastic overflow pipe

You can get an adaptor which looks like a rubber bung: it pushes into a standard waste socket and the overflow pipe pushes into a hole in the centre.

That's usually built into the boiler

[Not a serious suggestion] Run the condensate into your WC cistern and you'll have a self-descaling loo

[Christian McArdle]

Well, the steam won't know which way to go. Your preferred alternative will result in high pressure steam inside your cistern. Not a good idea!

It is normal to use 21.5mm overflow. It is superior to 22mm PEX/PB flexible pipe as it is more rigid, so easier to get a fall on horizontal runs. Check the boiler manufacturer if they really specify exactly 22mm. If they do, I'd probably go to 32mm, rather than use 22mm flexible.

Often they are included in the boiler. Check the boiler's instructions to check that the trap depth is sufficient to meet building regulations.

It is easy to make one with a few elbows, if one is really needed.

Sounds ideal.

Christian.

[Guy King]

The message from "Bodgit" contains these words:

If you have a pressure event it'll chuck scalding water and steam into the loo cistern. Could lead to a sudden evacuation.

[Bodgit]

Thanks all! Plastic overflow pipe it is.

Just one last question - Is 15mm copper pipe the best thing to use for the pressure relief outlet?

[Matt]

The relief valves are usually designed for 22mm copper (1" BSP if I recall correctly)

[John Rumm]

15mm on mine, so you had better check what the boiler instructions require.

[Matt]

Agreed, and always make sure it's connected from the earliest stages of pressure testing as it tends to make a bit of mess if it vents inside the property :-)

[Ed Sirett]

Almost all models have 1/2" or 15mm connections for the pressure relief valve and it's discharge pipe. The Vaillant VCW has 22mm and is almost unique in that respect.

[Matt]

Worcester Bosch use 22mm, I've seen what looks like an identical valve to the W-B on quite a few other makes as well - Glow-worm for a start.

[Ed Sirett]

Having fitted and serviced a number of models from both of these manufacturers I must have seen a different selection to you.

Off the top of my head: W_B 24CDi and 24 CDi junior - 15mm W_B 24SBi - 15mm W_B 30 CDi - 15mm

Which model did you mean?

We are tslking about the Pressure Relief Discharge Pipe not the condensate drain aren't we?

[Matt]

Definitely the pressure relief valve. Greenstar 25HE, 28HE, 30HE,

30HE Plus, 35HE Plus, 40HE Plus and probably some others.

The Glow-worm I'm not sure of but it was on a brand new install I saw only a few weeks ago.