Is it possible to get an exact co2 reading

[spikewt]

Hi

Just come away from a 22 year old Boulter oil boiler.
Carried out a service, the exchange and baffles were in quite a state. Cleaned it all up, then the burner, changed the burner nossel ect.
Pump pressure was at 8.5 bar and air setting was 3, MI's state 8 bar and 5.1 air set. Done a smoke test before any adjustments - 0 , but the co2% was at 7 where it should be 12.
So i set all the settings to MIs and that's when the poo hit the fan and it smoked and ran really bad.
Increase the air so no smoke but 9% is the highest it'll go before it goes right out.
Is it possible to get the right reading?

 

[thereisawizza]

When I trained for my oil 15 we had an old boy on the firm who would always leave the older boilers as they were found, bit like trying to bring a 25 year old piano up to concert pitch.....

 

[spikewt]

I remember them saying that when i done the burner training that some boilers just cant adjust but here's what's confusing me. Theres an analyser reading 18 months ago from another plumber which has every reading exactly bang on.
I just don't get it. Double checked the baffles aswell and they're all good.

 

[spikewt]

Just looking at a previous post, I'm wondering if it's a faulty new nossle now?

 

[PlumbBobBob]

could have the previous chap have just put what the readings were supposed to be not the actual readings?

 

[Jay The Plumber]

had a similar problem with a warmflow, the seal on the service hatch was knackered and was letting in a lot of clean air

 

[SimonG]

And don't set it to 12, otherwise you will be back to de soot it.

And on old boilers the settings in the books are a bit pointless.

 

[Best]

Be careful where you take the analyser readings. I had one where the reading taken from an original drilled test point in a twin wall flue was confusing me. I drilled a new test point in the single skinned vitreous enamel start off flue section and my guess proved correct as the reading was different.
Some old badly designed burners cannot be set much above 8 or 9% CO2, with a smoke number having to also remain high, but getting rarer nowadays. Some just need patience to fine tune them (nozzle assembly, adjustable flame ring diffuser, etc). They often came from factory without being set up, or clueless service engineers set them wrong.
Do replace your brand new nozzle if you think it could be faulty. Does happen occasionally that you get a faulty nozzle, or easily damaged.
If the previous service person only did their own hand written/typed analyser readings, then it could be nonsense. Some I came across with conventional vertical flues, had no test points but yet the previous engineer had given an analyser set of readings somehow and also amazingly perfect exact to the specs readings.

 

[Jay The Plumber]

And don't set it to 12, otherwise you will be back to de soot it.

And on old boilers the settings in the books are a bit pointless.

yea spot on, ive had a few where you pretty much have to close the air shutter completely to get the right CO2 and then the thing starts chugging and sooting.
with these I found there is a "flat spot" (thats the only way I can describe it) where the reading doesnt really change as you change the air setting, I usually listen to the burner in that setting area and leave it where it sounds good.. sorry, not very scientific but works.

 

[spikewt]

Thanks for all this advice. I'll go back to it tomorrow and increase the air slightly to bring the co2 down and bring it away from the point where it goes over. I'll change the nossle aswell just to be sure.
Thanks