R-Pro › Field cases › Heat pumps

Auxiliary Electric Heater (Backup Heater) Malfunction

Likely causes

Heater thermal fuse (72°C or 117°C) blown

Check: permanently opens after overcurrent or overheating

What to do: Turn off heater power, then measure resistance of thermal fuse and heating element: thermal fuse OL → replace; heating element resistance outside ±10% of rated → replace

Heater relay/contactor contact failure

Check: control signal normal but heater not operating

What to do: Measure heater relay coil voltage (AC220V) → if voltage is normal but contact is not closed, replace relay

No heater control signal output

Check: thermostat or main PCB output circuit failure

What to do: Locate manual-reset overtemperature thermostat button and attempt reset → if it trips again immediately, identify root cause (blocked discharge, heater overheating) first

Heating element (nichrome coil) open circuit

Check: infinite resistance when measured

What to do: Measure voltage at main PCB heater output terminal → if 0V, trace PCB or thermostat circuit

Overtemperature safety thermostat (manual reset type) tripped and not reset

Check: heater circuit remains open

What to do: Check dedicated heater circuit breaker in distribution panel → if tripped, measure heater insulation resistance (normal: ≥1MΩ) before resetting

Field tip

Fastest field check for blown thermal fuse: continuity test across heater terminals with multimeter — no beep (OL) means fuse or element is open. Always identify root cause (blocked airflow?) before replacing to prevent recurrence

All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.

Open R-Pro →

Related cases