Heat pumps are designed for efficient, reliable heating,cooling and hot water function. However, during operation, a heat pump may experience issues such as high-pressure protection, low-pressure protection, startup failure, compressor shutdown, or insufficient heating capacity.
One important point to remember is that the same error code can have different underlying causes.
Instead of immediately replacing components, a systematic diagnosis should start with water flow, airflow, refrigerant conditions, electrical components, and operating parameters.
Safety Notice: Electrical, refrigerant, and internal component checks should only be performed by qualified HVAC technicians. Always follow the manufacturer’s service manual and local safety regulations.
1. High-Pressure Protection
Typical Symptom
The controller displays High Pressure Protection or related error code and the compressor stops operating.
Possible Causes
High-pressure protection is often related to insufficient heat transfer.
Common causes include:
- Insufficient water flow
- Blocked water filter
- Partially closed valves
- Circulation pump malfunction
- Excessively high water temperature setting
- Scaling inside the heat exchanger
- Dirty outdoor heat exchanger
- Outdoor fan malfunction
Recommended Checks
- Check whether the circulation pump is operating normally.
- Confirm that the actual water flow meets the unit’s requirements.
- Make sure the water valves are fully open.
- Inspect and clean the water filter.
- Check the heat exchanger for scaling or blockage.
- Check outdoor fan operation.
- Inspect the outdoor heat exchanger for dust and debris.
Recommended Solution
Restore normal water flow and airflow before resetting the unit. For installations in hard-water areas, regular water-side maintenance is recommended to reduce scaling and maintain heat exchanger performance
2. Low-Pressure Protection
Typical Symptom
The controller displays Low Pressure Protection or related error code, and the compressor stops.
Possible Causes
Low-pressure protection may be caused by:
- Insufficient refrigerant charge
- Refrigerant leakage
- Incomplete defrosting
- Excessive frost on the outdoor coil
- Outdoor fan malfunction
- Dirty outdoor heat exchanger
- Restriction in the refrigerant circuit
- Operating conditions outside the unit’s design range
Recommended Checks
- Check refrigerant pressure and the overall operating condition.
- If insufficient refrigerant is suspected, check for leakage first.
- Inspect the outdoor coil for excessive frost.
- Check whether the defrost cycle is operating correctly.
- Check outdoor fan operation.
- Clean the outdoor heat exchanger if necessary.
- If required, check the refrigerant circuit for restrictions.
Recommended Solution
Do not simply add refrigerant without identifying the cause. If a refrigerant leak is confirmed, repair the leak first, then evacuate and recharge the system according to the manufacturer’s specified refrigerant type and charge.
3. Heat Pump Does Not Start
Typical Symptom
There is a heating or cooling demand, but the heat pump does not start.
Possible Causes
- Incorrect operating mode
- Incorrect temperature setting
- Power supply problem
- Circuit breaker activated
- Loose electrical connection
- Compressor contactor failure
- Compressor overload or thermal protection
- Control or communication problem
Recommended Checks
- Confirm the operating mode and temperature settings.
- Check the power supply and circuit breaker.
- Inspect electrical connections for loose wiring.
- Check the compressor contactor.
- Check whether the compressor has entered thermal or overload protection.
- Check the controller for additional error codes.
Recommended Solution
If a power supply or electrical connection problem is identified, correct it before restarting the unit.
If the compressor has entered thermal protection, allow sufficient cooling time and identify the reason for overheating before restarting.
4. Compressor Does Not Run
Typical Symptom
The heat pump has a heating or cooling demand, but the compressor does not start.
Possible Causes
- Abnormal power supply
- Compressor contactor failure
- Loose electrical connection
- Compressor overload protection
- Excessively high outlet water temperature
- Abnormal system pressure
- Protection signal from the control system
Recommended Checks
A qualified technician should check:
- Supply voltage
- Compressor contactor
- Electrical connections
- Compressor protection status
- Inlet and outlet water temperatures
- Refrigerant pressure
- Controller error history
Recommended Solution
Do not replace the compressor before identifying the root cause. In some cases, the compressor itself is not damaged. It may have stopped because of high pressure, overheating, abnormal voltage, or another protection condition.
5. Insufficient Heating Capacity
Typical Symptom
The heat pump is running, but the actual heating capacity is lower than expected or the target outlet water temperature cannot be reached.
Possible Causes
Insufficient heating performance may be caused by the heat pump itself or by the overall system design and installation.
Common causes include:
- Dirty outdoor heat exchanger
- Insufficient water flow
- Blocked water filter
- Insufficient refrigerant
- Refrigerant leakage
- Outdoor fan malfunction
- Excessive frost accumulation
- Poor pipe insulation
- Refrigerant circuit restriction
- Compressor performance issue
- Operating conditions outside the unit’s design range
Recommended Checks
- Clean the outdoor heat exchanger.
- Check circulation pump operation and actual water flow.
- Clean the water filter.
- Check the refrigerant system for leakage or abnormal pressure.
- Check outdoor fan operation.
- Inspect the outdoor coil for abnormal frost accumulation.
- Check water pipe insulation.
- Check the refrigerant circuit for restrictions.
- Compare the actual ambient temperature and water temperature with the unit’s design operating range.
Recommended Solution
When troubleshooting insufficient heating capacity, we recommend checking the following in order:
Water flow → Airflow → Heat exchangers → Refrigerant system → Compressor
In many cases, poor heating performance is not necessarily caused by the compressor.
Insufficient water circulation, dirty heat exchangers, inadequate pipe insulation, or operating conditions outside the system’s design range can also significantly reduce heating performance.
A Practical Troubleshooting Sequence
When a heat pump displays an error code or performance drops, follow this sequence:
① Check the Controller
Record the error code and operating status.
② Check the Water System
Confirm:
- Pump operation
- Water flow
- Filter condition
- Valve position
③ Check the Air Side
Confirm:
- Outdoor fan operation
- Heat exchanger cleanliness
- Frost condition
- Sufficient air inlet and outlet clearance
④ Check the Sensors
Compare controller readings with actual measured temperatures.
⑤ Check the Refrigerant System
If necessary, check:
- Refrigerant pressure
- Leakage
- Circuit restrictions
- Refrigerant charge
⑥ Check the Electrical System
Inspect:
- Contactors
- Relays
- Electrical connections
- Protection devices
- Control board
- Compressor protection status
Need Technical Support?
If you are an installer, distributor, HVAC contractor, or project engineer, providing the following information can help our technical team identify the problem more efficiently:
- Heat pump model and capacity
- error code
- Ambient temperature
- Inlet / outlet water temperature
- Water flow or pump status
- Refrigerant pressure, if available
- Installation photos or videos
- Controller display
Diagnose the problem correctly before replacing components. This can help reduce unnecessary maintenance costs and minimize equipment downtime.
