It is very common for air source heat pumps to stop working or enter "lockout" mode following a power outage. This is usually because the sudden loss of power—and the voltage surges that often occur when power is restored—can trip safety circuit breakers, blow internal fuses, or cause system computer errors.
Below is a step-by-step guide to troubleshooting and safely resetting your heat pump.
1. Check the power supply (circuit breakers and isolators)
Before assuming the heat pump is damaged, ensure it is actually receiving power.
1) Check the main fuse box/consumer unit: Look for any tripped circuit breakers. If you find a tripped breaker (usually in a middle position or showing a red indicator), switch it fully off and then back on again.
2) Check the local isolator switch: Most air source heat pumps have a dedicated pull-out isolator or circuit breaker, usually located near the indoor unit (e.g., in a utility room or cupboard) or on an external wall near the outdoor unit. Ensure it is in the "On" position.
3) Check the fuse: If your system is connected to a fused connection unit (a small switch containing a replaceable fuse), a power surge upon restoration could have blown the fuse. You may need to unscrew the cover to check if the internal fuse has blown.
2. Perform a "hard reset" (Crucial step)
Heat pumps contain sophisticated computers and compressors. When power returns, the system often enters a safety lockout mode to protect itself. You usually need to reset the system manually.
1) Completely cut power to the heat pump using the local isolator switch (not just the thermostat).
2) Wait at least 5 to 10 minutes. This is very important; it allows the internal compressor pressure to equalize and gives the computer memory a chance to fully clear its data.
3) Switch the isolator back on.
4) Listen for the system starting up. You should hear relays clicking, and eventually, the outdoor fan and compressor should start running.
3. Check the thermostat and controller
When power is restored, a surge current may reset the controller to its factory default settings.
1) Check the display screen on the indoor thermostat or controller. Are the time and date correct?
2) Check if the heating schedule/program has been cleared. If the system is in "Off" or "Holiday Mode" due to a settings reset, it will not start.
3) If the screen is blank, check if the thermostat needs new batteries or if the corresponding circuit breaker in the fuse box has tripped.
4. Look for error codes
If the system has power but is not running, check the display panel on the indoor unit (or sometimes the outdoor unit).
1) Are there any flashing indicator lights or error codes displayed (e.g., E01, F22, or a specific number of LED flashes)?
2) Note down the code and look it up in the user manual, or search online for the code along with your air source heat pump's brand and model. This will help you identify the exact cause of the safety lockout (e.g., low water pressure, sensor failure).
5. Check system pressure (if applicable)
If your heat pump is connected to underfloor heating or radiators, a power outage may have caused the system pressure to drop (or a pump failure could have led to a loss of pressure).
1) Check the pressure gauge on the indoor unit or the gauge on the boiler/manifold.
2) The pressure should typically be between 1.0 and 1.5 bar. If it falls below 0.8 bar, the heat pump will refuse to start to prevent damage. You may need to top up the pressure using the filling loop.
6. Consider power surge damage
If you have completed all the steps above but the unit still fails to start entirely (no lights, no display, no sound), an internal component may have been damaged by a power surge when the electricity supply was restored.
1) Blown internal fuse: There may be a high-capacity internal fuse on the main circuit board (PCB) that has blown to protect the system.
2) PCB damage: The main circuit board may have been fried by the power surge.
3) Compressor damage: In rare cases, a power surge can damage the compressor or its internal overload protector.
When to Contact a Professional
If you have checked the circuit breaker, performed a 10-minute hard reset, and confirmed that the water pressure is normal, yet the system still fails to start (or displays an error code that cannot be cleared), you should contact an HVAC technician or your air source heat pump installer.
Note: If there is a power outage lasting several hours during freezing winter weather, water inside the piping or the outdoor unit may freeze. If you suspect this has occurred, do not force the system to run, as this could cause the heat exchanger to rupture. Allow it to thaw naturally or seek professional assistance.
It is very common for air source heat pumps to stop working or enter "lockout" mode following a power outage. This is usually because the sudden loss of power—and the voltage surges that often occur when power is restored—can trip safety circuit breakers, blow internal fuses, or cause system computer errors.
Below is a step-by-step guide to troubleshooting and safely resetting your heat pump.
1. Check the power supply (circuit breakers and isolators)
Before assuming the heat pump is damaged, ensure it is actually receiving power.
1) Check the main fuse box/consumer unit: Look for any tripped circuit breakers. If you find a tripped breaker (usually in a middle position or showing a red indicator), switch it fully off and then back on again.
2) Check the local isolator switch: Most air source heat pumps have a dedicated pull-out isolator or circuit breaker, usually located near the indoor unit (e.g., in a utility room or cupboard) or on an external wall near the outdoor unit. Ensure it is in the "On" position.
3) Check the fuse: If your system is connected to a fused connection unit (a small switch containing a replaceable fuse), a power surge upon restoration could have blown the fuse. You may need to unscrew the cover to check if the internal fuse has blown.
2. Perform a "hard reset" (Crucial step)
Heat pumps contain sophisticated computers and compressors. When power returns, the system often enters a safety lockout mode to protect itself. You usually need to reset the system manually.
1) Completely cut power to the heat pump using the local isolator switch (not just the thermostat).
2) Wait at least 5 to 10 minutes. This is very important; it allows the internal compressor pressure to equalize and gives the computer memory a chance to fully clear its data.
3) Switch the isolator back on.
4) Listen for the system starting up. You should hear relays clicking, and eventually, the outdoor fan and compressor should start running.
3. Check the thermostat and controller
When power is restored, a surge current may reset the controller to its factory default settings.
1) Check the display screen on the indoor thermostat or controller. Are the time and date correct?
2) Check if the heating schedule/program has been cleared. If the system is in "Off" or "Holiday Mode" due to a settings reset, it will not start.
3) If the screen is blank, check if the thermostat needs new batteries or if the corresponding circuit breaker in the fuse box has tripped.
4. Look for error codes
If the system has power but is not running, check the display panel on the indoor unit (or sometimes the outdoor unit).
1) Are there any flashing indicator lights or error codes displayed (e.g., E01, F22, or a specific number of LED flashes)?
2) Note down the code and look it up in the user manual, or search online for the code along with your air source heat pump's brand and model. This will help you identify the exact cause of the safety lockout (e.g., low water pressure, sensor failure).
5. Check system pressure (if applicable)
If your heat pump is connected to underfloor heating or radiators, a power outage may have caused the system pressure to drop (or a pump failure could have led to a loss of pressure).
1) Check the pressure gauge on the indoor unit or the gauge on the boiler/manifold.
2) The pressure should typically be between 1.0 and 1.5 bar. If it falls below 0.8 bar, the heat pump will refuse to start to prevent damage. You may need to top up the pressure using the filling loop.
6. Consider power surge damage
If you have completed all the steps above but the unit still fails to start entirely (no lights, no display, no sound), an internal component may have been damaged by a power surge when the electricity supply was restored.
1) Blown internal fuse: There may be a high-capacity internal fuse on the main circuit board (PCB) that has blown to protect the system.
2) PCB damage: The main circuit board may have been fried by the power surge.
3) Compressor damage: In rare cases, a power surge can damage the compressor or its internal overload protector.
When to Contact a Professional
If you have checked the circuit breaker, performed a 10-minute hard reset, and confirmed that the water pressure is normal, yet the system still fails to start (or displays an error code that cannot be cleared), you should contact an HVAC technician or your air source heat pump installer.
Note: If there is a power outage lasting several hours during freezing winter weather, water inside the piping or the outdoor unit may freeze. If you suspect this has occurred, do not force the system to run, as this could cause the heat exchanger to rupture. Allow it to thaw naturally or seek professional assistance.
