You may have read the electric heating topic in which I complained that my PHEV on a 10A UK cable used ONLY the battery for preheating even though it was connected to mains.
Well, after a bit of messing about I think I've worked out it is a bug in the car's software and it will probably affect those with a 16A charger too.
If you have the charging set to timer either because you get cheaper electricity in the early hours or you do this as it is best for the grid then when you use the preheater it will heat from battery. If you do not set the charging timer then when you choose preheat it will at the same time start drawing power from the mains, even with my 10A charger. I realise it may still use more power than the mains can supply (4KW used against 2.75KW mains) but the difference is minimal.
The setting I had previously tested was to allow charging between 1am and 10am, with the preheater to start at 7.45. In this setup the heater used just battery. Even manually selecting the heater didn't take power from the mains.
My guess is that once the battery is charged, it transitions to "waiting to charge" mode even though you are within the allowed charging schedule and doesn't allow mains to be used for preheat.
This is an easy fix for myself as I will just use a timed outlet to achieve the same thing. Anyone with off peak electricity and that intends to preheat should check this out. Do the 16A charge points allow a charging schedule or is it entirely down to the car
Outlander PHEV GX4h
Pearlescent White, Protection Pack
Front & rear sensors, LED Side & Running Lights
Rear DVD & Media player, Roadhawk HD Dashcam
Steelmate TP-70 TPMS
Nokian WR SUV 3 winter tyres & spare alloys