Trainee gas questions in this thread ONLY please

[AWheating]

[DLMURL]http://www.radmidlands.co.uk/Downloads/ControlsDom.pdf[/DLMURL]

page 6

https://docs.google.com/file/d/0B6zTTicYyEudZnhHUVlSRnI5cVk/edit

another good source of info for guys learning the trade.

 

[combo]

Vaillant ecomax says you must have 17-25 mb at P1...this is to check the meter/pipework can supply the correct volume of gas at full working pressure. The vacuum created by the fan to premix the burner does not affect the P1 value, it only affects the P2 value ie a negative pressure........Am I right in saying this ?

 

[combo]

I guess what im saying is, these low mb inlet pressures are to allow for the usual possible pressure losses such as; 2mb WP, 1mb pipeloss, and the possible loss across meter at peak network...its nothing to do with the air/gas valve.

 

[AWheating]

yes your correct that the p1 (inlet) reading should not be effected by the way the gas valve uses the gas. No matter what the situation you are not allowed more than a 1mb drop from the meter test point to the point of connection at the appliance. The manufacturer may state its internal pipework and filters will show a 1-2.5mb drop from this conection to the inlet test point at the gas valve. But this manufacturers drop can not be used to avoid correctly sizing of the gas supply.

so i think for a WB you could have 19mb working pressure, 1mb drop on pipework, 1.5mb drop inside the appliance giving you a min working pressure of 16.5mb as required in the instructions.

 

[Barry98]

For trainees to ask questions prior to passing gas safe

 

[Dotty]

Thread from open forum merged in. Sorry Lee, it's bumped your post down!

 

[bassmonster]

Unsafe situation? It only has a rubber seal on the outside but not cemented inside.....

 

[kirkgas]

Depends on MI of specific boiler, some allow rubber collar to be used as weather seal, only required on the outside to stop POC's re entering property and going up cavity, inside seal is only for decor

 

[bassmonster]

Thank you Kirk. I'll have a nosey in the MI to be sure

 

[albatross]

Unsafe situation? It only has a rubber seal on the outside but not cemented inside.....

View attachment 17879

View attachment 17880

If neither wall is cemented its at risk. Flue must be sealed to the building with cement.(not expanding foam/silicone. Also flue must be adequately supported and the rubber will not do that and just being attached at the boiler is not good enough. If it was low enough some flues could work loose/ be pulled out causing fumes to go into the room if not securely cemented in.

 

[Killy Bing]

If neither wall is cemented its at risk. Flue must be sealed to the building with cement.(not expanding foam/silicone. Also flue must be adequately supported and the rubber will not do that and just being attached at the boiler is not good enough. If it was low enough some flues could work loose/ be pulled out causing fumes to go into the room if not securely cemented in.

reminds me, i have a flue i need to go fit....
damnit

 

[tamz]

If neither wall is cemented its at risk. Flue must be sealed to the building with cement.(not expanding foam/silicone. Also flue must be adequately supported and the rubber will not do that and just being attached at the boiler is not good enough. If it was low enough some flues could work loose/ be pulled out causing fumes to go into the room if not securely cemented in.

Depends on the manu. Worcester and vaillant don't care much but baxi and vokera want it sealed.
Common sens says mix up some compo but common sense also says i've more chance of having a heart attack humping Kylie than anyone ever being at risk of anything.

 

[kirkgas]

Albatross, EVERY un cemented flue isn't AR, you need to be boiler specific when you say that as some manufacturers allow the rubber seal, in fact (can't remember make model) I remember we fitted some boilers in 5 high flats and chose the boiler as we could fit the flue and rubber seal from the inside, I'm sure we had to drill 6" hole rather than 5" to accommodate rubber ring going through from inside, I've always done what manufacturer said, but on contracts where we had builders on site anyway I always got them to cement the flue holes, but I wasn't paying for a 5 high scaffold to seal them when I could choose a different boiler and fit flue from inside, the wall on the inside is only for decor, if the flue corrodes the POC's would go up the cavity, and any fumes blowing back in from outside would always go up the cavity rather than right back into the house

 

[albatross]

Albatross, EVERY un cemented flue isn't AR, you need to be boiler specific when you say that as some manufacturers allow the rubber seal, in fact (can't remember make model) I remember we fitted some boilers in 5 high flats and chose the boiler as we could fit the flue and rubber seal from the inside, I'm sure we had to drill 6" hole rather than 5" to accommodate rubber ring going through from inside, I've always done what manufacturer said, but on contracts where we had builders on site anyway I always got them to cement the flue holes, but I wasn't paying for a 5 high scaffold to seal them when I could choose a different boiler and fit flue from inside, the wall on the inside is only for decor, if the flue corrodes the POC's would go up the cavity, and any fumes blowing back in from outside would always go up the cavity rather than right back into the house

It is. Gas Regs say a flue must be supported and there must not be an opening in the building within 300mm.

You can do what you just said as long as you cement the inside course and just have the rubber outside. Then you have supported the flue and sealed it. I have done it too.

 

[Mike Jackson]

Gas Regs don't. Building regs do but MIs supersede building regs.

 

[tamz]

This one has been done to death in neumerous posts.

 

[kirkgas]

It is. Gas Regs say a flue must be supported and there must not be an opening in the building within 300mm.

You can do what you just said as long as you cement the inside course and just have the rubber outside. Then you have supported the flue and sealed it. I have done it too.

So are you agreeing or disagreeing with me?
First you said I'm wrong then you said you did the same, if the outside hole isn't cemented is it AR? I said no and you said it was

 

[bassmonster]

Here's another Flue photo. The hole above is for an extractor fan which isn't working. Am I right is classifying the pipe as ncs as it's too close to the flue? Also the hole above, ncs or AR?

 

[albatross]

So are you agreeing or disagreeing with me?
First you said I'm wrong then you said you did the same, if the outside hole isn't cemented is it AR? I said no and you said it was

I'm saying It's ok to do and I've done it as long as you cement one side, either inside or out, it doesn't matter which.

Best practice is cement both inside and out.

High level jobs cement the inside. It will support and hold the flue, comply with not allowing an opening within 300mm of a terminal and stop draughts. Leaving gaps won't help with gas bills.

Then you can sleep at night knowing no one can question your work/call you back. In our job it's not worth sitting in a grey area, cover your backside for an easier life. I'm here to give good advice, not argue and fall out. Even if something is not written down in law or MI's it's worth erring on the side of safety and doing little things like mixing a bit of cement.

 

[mutley racers]

[DLMURL]http://www.radmidlands.co.uk/Downloads/ControlsDom.pdf[/DLMURL]

page 6

https://docs.google.com/file/d/0B6zTTicYyEudZnhHUVlSRnI5cVk/edit

another good source of info for guys learning the trade.

Can't seem to open that bottom one