Martin Brown wrote:

Where were you measuring the greenhouse air temperature though. If it
was against an outside wall then that might be accurate. Yesterday was
extremely cold down to -7C here so under powered heaters will struggle.

The themometer (in/out - max/min) is well away from the outside walls and
the greenhouse is well insulated with bubble plastic. I think the reading
was reasonably accurate.

A separate thermostat somewhere near the plants you most want protected
is the only half way reliable method. The one inside the heater is to
easy to satisfy (and some modern ones have it a daft location).

Seems the best solution - will have a look around. Thanks for your help.
--
Regards,

Troy the Black Lab.