Extending a horizontal flue problem

[KevinRochford]

Hello everyone, hope you are all good.
I’m having a problem extending the horizontal flue.
I have built an extension and want to extend the horizontal flue by 4m. The boiler is a Baxi NetaTec 33GA and in the specs it says a 60/100 flue length up to 10m with a deduction of 1m per 93 degree bend and 0.5m per 135 degree bend
My calculation is 4m tube, 1x93. 2x135 = 6m which is well within tolerance.
My problem is when I connect the 93 degree to the boiler then 0.5m extension through the wall, then 2 135 degree bends it all works, steam is coming out and hot water works. As soon as I put the first 1m extension onto this the boiler stops working, the water goes up to 39degrees and back down and will never go past 39.
Does anyone have any advise please?

 

[CBW]

Hello Kevin,

Are you gas safe registered? If so this need some to be asked in the combustion chamber forum not an open public one. If not then I doubt very much you’ll get gas related advice - it’s against forum rules.

 

[KevinRochford]

Hello novice, I’m not gas safe registered and I wouldn’t have touched the settings or mechanics of the boiler, that’s for the professionals. However extending a flue should be simple and I will get someone to look at it that’s gas safe as I am having problems doing it myself, I was just wanting to know why it stopped working when I connected the first 1m extension

 

[Madrab]

Hi @KevinRochford unfortunately you shouldn't be touching anything to do with the boiler flue, unless you are gas safe registered. It's a recipe for disaster as you may not have the experience nor the equipment to ensure that the boiler is running properly and not dangerous once it's all back together and running.

You won't receive any advice with anything gas related like that in the public forum I'm afraid, its the DIYnot rules.

 

[ScottishGasMan]

Yea, the flue is literally the most important part of being safe (its the bit that kills folk when its done wrong) so turn off the boiler, call a gas man, and enjoy being alive come Christmas time.

 

[KevinRochford]

Thanks for the replies, from reading a few other posts on here I think I’m right in thinking that extending the flue can affect the combustion chamber which is probably why I was having problems when I start extending.
Not something I will touch but happier I know the reason.