I have the same problem as the OP. My heater never gets hot, and only consumes about 0.5 - 1 kWh. The outside temp has been about 40°F.
Also, once I turned on the A/C and the kWh dropped to 0 and it blew cold, moist air (fogged up the windshield). I turned A/C off and it jumped back up to about...