If this heater is plugged into a 240V volt outlet, the PCBA will cut off the heating and fan immediately, it will show a "UH" error code and , and the heater has to be unplugged. The heater will only work properly when it plugs in the right voltage.
This is a temperature sensor (probe) error. When this code shows, the heating element and fan are turned off, heater needs to be unplugged and check the temperature sensor which could be loose or dis-connected or damaged.
Program malfunction. You will need to unplug and plug in heater again. If this error still persists after several tries, The PCBA needs to be replaced.