Sharp AR-M237 Error Code H4-21

-H4-21 means:Sub heater lamp abnormally low temperature detection. The setup temperature (about –25°C: Sim 43-1-1) is not reached within the specified time (about 32sec) from turning on the power ON SW. (When the temperature falls below 140°C in the standby mode.)
-Causes:
Sub heater thermistor defect
Sub heater lamp failure
Sub thermostat failure
Control PWB failure
-Check the sub heater lamp blinking with SIM 5-2-2.
When the lamp blinks normally: Check the thermistor and the harness. Check the MCU PWB thermistor input circuit.
When the lamp does not light: Check for disconnection of the heater lamp and thermostat. Check the interlock switch. Check the power PWB and the MCU PWB lamp control circuit.
Clear the display of self-diagnostics with SIM 14.
The H4 errors will not reset by themselves. You must enter service mode to reset this error even if the problem has been repaired. The reset process is outlined below (DO NOT USE ANY OTHER FUNCTIONS IN SERVICE MODE):
Press the following sequence: "#/P" "*" "C" "*"
Type in 1 4
Press start
hit 1 for yes
hit start
Unit should power off and the restart.
If the error code recurrs ther are other problems.

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