Hello all,
I have had quite a few Honda & Mitsubishi sensors with intermittent heater circuit faults & usually just change them with genuine units(usually denso which I can get from our local factors a lot cheaper than dealer).
I usually measure the current at the sensor, which confirms the supply & ecu ground at the same time if current is flowing, then I check supply & ground if no current flow. Quite often they are working when I check them & will do the same as yours, sometimes not bringing the light on for two weeks, so if a code comes up for heater circuit, I normally just change the respective sensor.
Regards, Andrew