Potterton promax 15/2 he plus combustion issue

[leedsgasservice]

Hi, I'm after some advice regarding the above boiler. Personally I've never come across this model as I mainly work with commercial boilers.
The problem I'm experiencing is when the boiler has been running for about 20 mins it will just go out and then re light with a bit of a pop. Im the 3rd engineer to visit now and the boiler has had the pcb and flue fan replaced.
Connected manometer and working pressure is 19mb and never seems to move from that.
Now the interesting part, when the boilers running the flue analyser reads, 8.9%co2 and around 5%O2 . After around 15mins or so I notice the co2 increase to 11.8% and the O2 drops dramatically to 0.2...0.1 then goes out.
When I observe the flame picture it seems to turn green then lifts off the burner then goes out. It's as if its combustion gases are entering then air box.
I've replaced then burner door and fan seals and checked the flue seals in the elbow. I also dropped the combustion box base and checked that seal,all ok apart from alot of debris.
Also with the air box door removed it still burns really bad and goes out.
I'm confused. I did read that the ceramic burner could be damaged,but all seems in tact and fairly clean.

Any help would be appreciated.
Thanks,matt.

 

[Billy Bob Bob]

i would double check the burner they can fail when hot and lift from there cradle

 

[leedsgasservice]

Ok,I'll have another look but all seemed ok and the ceramic burner didn't move at all.
Might take a new one with me just in case. Thanks for the swift response.

 

[Billy Bob Bob]

do a search on here BAXI Barcelona or BAXI 133 he same set up,its true and very frightening what the op says seen it happen very dangerous boilers be warned

 

[yo1]

is this caused by a problem with the burner, the gauze on the burner or something?

 

[Billy Bob Bob]

to helpful for my own good i am ,read this its the same fundamental boiler regardless if its a heat only or combi http://www.ukplumbersforums.co.uk/c...erheats-melts-heat-exchanger-explanation.html

 

[leedsgasservice]

Yea,that's the post I read the other day regarding this type of burner. It's a bit like a plaque heater when they crack,then after a few minutes bang and a blow them selves out. A bit of a party trick for the old assessors down at ngst in leeds. Haha.:lol:
The puzzling thing for me was that the flame begins to fade and lift off the burner,not to mention it being bright green. I suppose each burner could fail differently and as I said before the analyser readings go way out.

 

[gasmarc]

I knew a really experienced potterton engineer and he told me to avoid them at all cost apparently the flues can rot out on them, good luck

 

[leedsgasservice]

Cheers for that,I'll double check the flue again. I can't be beaten by this piece of junk. As a customers once said to me "it's a flame in a box,how hard can it be"?.