Daikin Heat Pump Error Code P4

P4 indicates an abnormality in the radiation fin thermistor circuit on the outdoor unit. This thermistor monitors heat exchanger fin temperature to protect internal components from overheating. The fault can stem from a failed sensor, damaged wiring, or a defective main PCB in the outdoor unit. The system shuts down when this error is detected to prevent further damage.

No. The P4 error causes the unit to shut down because the system can no longer reliably monitor heat exchanger fin temperatures. Attempting to bypass or override this fault could allow the outdoor unit components, including the compressor and inverter board, to overheat and sustain permanent damage. The unit should remain off until the fault is diagnosed and resolved.

A power reset may temporarily clear the P4 code, but the error will return if the underlying fault in the thermistor circuit has not been corrected. Resetting without repairing does not fix the sensor, wiring, or PCB issue that triggered the fault. Repeated resets without addressing the root cause can also mask the problem and allow conditions that may damage other components.

Basic checks such as inspecting the thermistor connector for looseness or visible corrosion are within reach for a knowledgeable DIYer. However, testing thermistor resistance values, tracing wiring faults, and replacing the outdoor unit main PCB require disassembly of the outdoor unit and familiarity with electrical diagnostics. Most homeowners should call a qualified HVAC technician for this repair.

Repair costs vary depending on the root cause. If only a thermistor replacement is needed, parts and labor combined typically range from around $100 to $250. If the outdoor unit main PCB requires replacement, costs can range from $400 to $900 or more depending on the specific model and labor rates in your area. Diagnosing the fault before ordering parts helps avoid unnecessary expense.