Unvented cylinder discharge pipe

[peter7463h7]

We recently had a 120 litre Gold unvented cylinder fitted in our first floor airing cupboard. The cylinder's pressure release valve D2 discharge pipe is plastic (originally fitted for the previous twenty year old BoilerMate) and looks about 22mm diameter. There is approx 100mm of vertical section discharge pipe between the tundish and the first 90 degree bend. There are two such bends before a straight run of pipe (with a nice looking fall) about two metres long that goes behind the bath and through the external wall and exits over a concrete path in our garden at a height of about 2500mm. British Gas inspected this last week and refused to insure the central heating under their Homecare plan (a) because of the plastic pipe, and (b) because the pipe exits over a walkway. Their inspector also wasn't happy about the 100mm vertical section between tundish and first bend. The plumber who fitted the cylinder has suggested replacing the D2 with copper (not sure what size he intends using, I'm assuming 22mm is a minimum) and turning the pipe towards the wall where it exits. Not sure what his plan is regarding the 100mm vertical section (I now realise this should be 300mm minimum, though I can't see how he can achieve this as there's precious little vertical room to manoeuvre in the airing cupboard).


I can't see any reference to turning the pipe towards the wall in the G3 building regulations. Is this an acceptable way to terminate the discharge pipe?


Also, just how critical is the 300mm minimum vertical drop between tundish and first bend?


Thanks

 

[Meady]

*If the pipe exits up high he must brim it down to the ground and fit a cage Over the end of the pipe, *there must be 300mm between the tundish and the first elbow
*the plastic pipework must be capable of carrying high temperature water and not just standard plastic

 

[stevetheplumber]

back to wall terminations are only allowed in exceptional circumstance and i think you have to get building controll permission

 

[wild nomad]

Hi Peter,

The reason why the BG Engineers didn't like the D2 termination area is because the water that comes out could potentially be scolding hot and constitutes a danger to anyone walking under it. Extending the pipe down so it is no more than 100mm off the ground, terminates close to the wall and is covered by a guard or cage that maintains visibility should sort it.

The D2 pipe (below the tundish) should be at least one size larger than the D1 pipe (that's the pipe above the tundish) so 22mm should be sufficient so long as the D1 pipe is only 15mm. The effective length of the D2 pipe at 22mm can't be more than 9m long. That includes the resistance of the fittings as well - each elbow equates to 0.8m. This means that if you have 3 elbows (2.4m equivalent) on your D2 pipe run then you can only have 6.6m of 22mm copper pipe. Make sense?

The regulations state that the D2 pipe should be of a material capable of taking high temperature water, which some plastic pipes are, but it also contradicts itself and states that it should be metal pipe. To be safe, take the plumbers advice and use copper. Turning it into the wall isn't enough though, it needs to terminate low down.

Where the pipe goes through the wall it should be sleeved to protect it. Plastic pipe should be good enough for this.

Not sure what to suggest in order to accomplish 300mm of vertical pipe below the tundish without seeing it. It does definitely need to be 300mm though if it is to comply with G3 building regs.

The bottom line is that the system is not that old and does come under current building regs. With that in mind the people who originally installed it have a responsibility to come round and fix it free of charge since the job you paid them for hasn't been completed!

Hope this helps.

 

[SimonG]

What paperwork did you get for the install. Sounds like somebody has installed it who shouldnt have.

The sad thing is that you dont even have to refer to the g3 regs, as all the necessary info is in the installation manual. RTFM.

 

[wild nomad]

SinonG is right. Everything you need to know is in the manufacturer Instructions which the installers should have given you after the job.

Irony is, is that I have come across British Gas installs that contravene all sorts of building regs

 

[Dotty]

From the logic training course notes. Doesn't say owt about LABC permission being required. I wouldn't bother asking.

 

[iiplumbing]

Also, just how critical is the 300mm minimum vertical drop between tundish and first bend?


Thanks

At full volume discharge the water will back up if there isn't sufficient fall between the outlet of the tundish and the first bend.

I can't see how a large cylinder airing cupboard cant accommodate this 300mm fall especially if it is then running under a bath?

If you can connect the discharge from the tundish to the waste pipe under the bath (provided it can withstand 100degC water) you may wish to connect the TRV/PRV with a product called Hotun.

This product has been designed to be both a tundish and a odour trap to prevent foul odours coming back up from the waste pipe. The product has an internal drop sprung seal inside it.

It only costs at list £22.60 and trade it should sell for about £15.85+vat

Fitting Hotun enables you to do away with the external discharge pipe altogether.



If you have any questions please feel free to ask

regards

Russ

 

[kirkgas]

English building regs list the back to wall discharge termination as the least liked, but it is still an approved method, and just a note on it, the gap between the wall and the end of the pipe needs to be at least the same size as the pipe itself to allow water to discharge freely

 

[Reg Man]

Who ever fitted it, needs to come back and fit it according to the standard at there cost. no excuses for such deviations from standards. If it were to discharge it could give someone a scalding hot shower.

 

[chris watkins]

From the logic training course notes. Doesn't say owt about LABC permission being required. I wouldn't bother asking.

Take care croppie this is only logic's interpretation!
Nowhere does it say that the discharge (D1) pipework from the expansion relief is limited to 600mm !!! that limit applies only from the T&P valve.

I am going to guess that is why the OP thinks it is not possible to achieve the min 300mm vertical below the tun dish on a 120L Gold.

And yes it is important to have at least that, want to no why ? Pull the T&P safety valve, peter, as is required to test it from time to time (this would happen if it went off under high temperature condition)!!!

As others have said get the installer back & ensure that they have registered the installation as required by the Building Reg's if they have not, unfortunately it is you that has broken the Law.

 

[chris watkins]

At full volume discharge the water will back up if there isn't sufficient fall between the outlet of the tundish and the first bend.

I can't see how a large cylinder airing cupboard cant accommodate this 300mm fall especially if it is then running under a bath?

If you can connect the discharge from the tundish to the waste pipe under the bath (provided it can withstand 100degC water) you may wish to connect the TRV/PRV with a product called Hotun.

This product has been designed to be both a tundish and a odour trap to prevent foul odours coming back up from the waste pipe. The product has an internal drop sprung seal inside it.

It only costs at list £22.60 and trade it should sell for about £15.85+vat

Fitting Hotun enables you to do away with the external discharge pipe altogether.

View attachment 20139View attachment 20140

If you have any questions please feel free to ask

regards

Russ

Has this been approved for use on un-vented system discharge pipework Russ ???
If not, if not it cannot be used !!!!!

 

[iiplumbing]

Has this been approved for use on un-vented system discharge pipework Russ ???
If not, if not it cannot be used !!!!!

approved by who Chris?

as the regulations stand the product does not have to be approved by anyone! Having said that it does have to comply with 7 regulatory provisions or be no less effective than the guidance given.

This product complies with all relevant regulations and it temperature rated to 100degC

if someone wants to find out more details then please pm me and I will provide ALL compliance documentation

back to Chris, who would you want it "approved" by and I'll let you know what the status is at this time

cheers

russ

 

[Best]

I bet the 300mm minimum from D2 pipe to first bend is not there because either the D1 pipes are configured too low or/and the D2 has been angled up to too high a position.
The exam I redid recently clearly says the discharge through a wall at, in this case 2500mm high, must be run to within 100mm off the ground with a cage or more ideally into a gulley above the water level but below the grate. As far as I read it, no cage required if discharge fully inside gulley.

 

[tolly]

Russ, does that tundish rely on the weight of the water to compress the spring, and push down the rubber to allow water to get flow into d2?

If so, do you think it will still operate in years to come when the spring potentially scales up?