High PPM on low rate when servicing Vokera Unica i28

[MarcusA]

I was wondering if anyone can help with this. On servicing a two year old Vokera Unica i28 I carried out combustion analysis checks. The high readings were fine but when I checked on low I was only getting 6% CO2. When I slowly started to adjust the valve I couldn’t get the Co2 anywhere near the manufacturers requirements of 9% without the ppm going through the roof. I had the same issue with the same boiler last year and fitted a new gas valve which resolved the problem at the time. However it has happened again this year and I’m not sure what the problem could be. The boiler is still quite new so vokera’s advice to clean the heat exchanger doesn’t make sense to me.

 

[ShaunCorbs]

How old ?

 

[MarcusA]

It’s only 2 years old. I service quite a few of these Unica i28 boilers of the same age and have no issues.

 

[ShaunCorbs]

Should be under warranty then ?

 

[MarcusA]

The housing association I work for only get one year warranty with these boilers.