[russellb]

Thanks, I've checked the wiring (again) and can't find any errors.

Hello russellb,

I pretty sure that I have the same type of display running here perfectly (despite of the additional touch rotation) and I had similar problems at the beginning due to a wrong connection.
Could you please provide the Pin connection between the RX pin header and the display pin header. 
Eg. SCK <-> SCK
Then I would crosscheck with my connection.

Regards,
engolling

Thanks engolling,

I've checked at least 3 times with http://www.meteocercal.info/forum/Thread...77#pid5677, including checking end-to-end resistance, and all correspond to that schema.

I have a "wireless display board" to use the second screen on, so I'm just building that up, and will see if that behaves any differently.
I've also been exploring the arduino forums to see if I can find any more data on the board.
I can see it has an HR2046 chip as U2.

At least in my exploring I found a test sketch for the BME280 which appears to be giving realistic results.

Regards
Russell