Gas Combi Boiler Pressure Relief Pipework & Building Regs

[Mitch]

I had a gas safety check on a Bosch 24i combi and the man said that the pressure relief pipework was sub-standard as it simply runs from the boiler to the floor with the exit inside rather than an external exit.

Can someone please tell me what the Building Regs require as I am thinking of correcting this myself (especially as the main work is do drill a hole)? EG is it 15mm or 22mm pipe, what are restrictions on the exit, such as is it downward facing etc etc.

Also where could I read or access these regs?

I even have the original Bosch Installation instructions but they dont mention this pipework beyond the boiler

Thanks

Simon

[John Stumbles]

I don't know which regs cover it - it certainly should be in the manufacturer's installation instructions - but it should terminate outside a few inches from, and facing, the ground; so that if/when the pressure relief valve opens the blast of potentially boiling water + steam can hit the ground without injuring anyone. 15mm is generally used.

-- John Stumbles

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[Kalico]

It is 15mm pipe and easy enough to do yourself. The pipe runs outside then is supposed to go to within a few inches of the ground, but if the boiler is high up in your building, that may not be practicle, so use common sense that any escaping HOT water will not spray over anyone below. HTH ROb

[BillR]

Yes, they are normally 15mm. The hole should be drilled so there is a slight slope downwards from inside to outside. On the outside its normal for the outlet to be turned back towards the wall with say a 90 and a 45 degree bends. This is to avoid scalding anybody who may be near the outlet when the relief valve lifts.

[Mitch]

Thanks for advice - let the drilling commence!

[andrewpreece]

Don't know about regs but my Vaillant (28kW) instructions say that it must vent outside, must be as short as possible, not lesss than 15mm diameter, with a continuous fall away from the boiler [ since it doesn't specify a slope, in effect I took it to mean that the pipe shouldn't actually go uphill at any point ], that the vent should terminate in a position which would not cause a hazard to persons due to discharge of water or steam, nor cause damage to any electrical components or external wiring, and the point of discharge should be clearly visible.

My old combi position was a first floor bedroom, and the vent exited the cavity wall horizontally about 20 feet up. I've just installed a new combi in my old outside loo and have the discharge pipe exit the wall, and immediately turn through 90 degrees and discharge into a gully at the side of the house.

Andy

[IMM]

Not quite. 15mm pipe, outside at a low level and the pipe being turned into the wall using an elbow. If boiling water/steam is lets off it hits the wall. The pipe need not be sleeved going through the wall.

[IMM]

Also you can terminate inside a garage (integral garage or not). There again at low level and the pipe turning into the wall. It can terminate onto a flat roof too, one gains at low level and turning into the wall.

[IMM]

The pipe can drop down inside and penetrate the wall at low level to the outside. External pipes can look very ugly.