EnviroPlus gas sensor problem


I’m having a problem with the oxidised gas reading on my enviro plus.

It has a high base line level, 8700 ish, and only very minor fluctuations

I managed to borrow one from a friend and e.g. when his went from 11037 to 6696 mine went from 9712 to 9096.
As well as a much flatter line, mine never seems to drop below the high base line.

Any ideas?

My code is at https://github.com/wrighting/enviroplus-aws and the comparison readings are on line although I’m not going to share the url in public.