Thank you for your responses. May be I have achieved what I thought was impossible. I have cleared the data of my card and am looking forward to see what will happen tonight.

The last two nights produced an AHI of zero. Normally my AHI ranges between 0.3 to 1.5. I can't believe this is right. I have downloaded the data in ResScan and the AHI does not even show in the detailed graph which increases my suspicion that this is incorrect. Has anybody seen this before?

I must be the luckiest man alive: my climateline has been working flawlessly for nine months now