Heat pump error codes
An error code tells the engineer where to look. The common ones are about water flow: L9 on a Mitsubishi Ecodan and 7H on a Daikin Altherma both mean the water isn't moving through the unit fast enough, usually low pressure, a blocked filter or air.
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- L9Ecodan: low primary flow
- 7HDaikin: abnormal water flow
- U0Daikin: short of refrigerant
- 1 resetthen book a repair if it returns
Ecodan error codes
| Code | What it means | What it usually is |
|---|---|---|
| L3 | Circulation water overheat protection | Flow too low or the water too hot. Check the filter and pressure. |
| L5 | Indoor temperature sensor failure | A sensor (THW1 or THW2) needs testing and replacing. |
| L6 | Circulation water freeze protection | Water too cold in the unit. Check the flow and the outdoor unit. |
| L8 | Heating operation error | The system isn't reaching temperature. Needs a look. |
| L9 | Low primary flow rate | The most common call: low pressure, a blocked magnetic filter, air or a pump fault. |
| LP | Water flow out of range for the outdoor unit | Flow too low or too high through the outdoor unit. |
| P1 | Room temperature sensor failure | The room sensor (TH1) needs testing. |
| P6 | Anti-freeze protection of the heat exchanger | Low flow in cold weather. Check the filter and pressure. |
| E0 to E5 | Lost contact: main controller and the control board | Wiring or the controller. |
| E6 to EF | Lost contact: control board and the outdoor unit | Wiring, power to the outdoor unit or a board fault. |
| U and F codes | Outdoor unit failure | An engineer reads the outdoor unit's own code. |
From Mitsubishi Electric's own FTC controller tables. To clear a code, the manual has you switch the system off or press F4 (RESET) on the main controller. A code that comes back needs an engineer.
Daikin Altherma error codes
| Code | What it means | What it usually is |
|---|---|---|
| 7H | Abnormal water flow | Low pressure, a blocked filter, air or a stuck pump. |
| 80 / 81 | Inlet or outlet water sensor fault | A sensor needs testing or replacing. |
| 89 | Water heat exchanger freezing | Low flow in cold weather. Check the filter and pressure. |
| AA | Backup heater overheating | The backup heater's thermal cut-out has tripped. |
| C0 | Flow sensor or flow switch fault | The flow sensor needs testing. |
| E1 | Control board (PCB) defect | Needs an engineer. |
| E3 / H3 | High pressure switch | Often low flow or a blocked coil. Needs an engineer. |
| U0 | Shortage of refrigerant | A gas leak. Needs an F-gas certified engineer. |
| U4 | Indoor and outdoor units not talking | Wiring, power or a board fault. |
| UA | Indoor and outdoor units don't match | Usually after a part was replaced. |
From Daikin's own Altherma tables. Daikin codes often have a number after them (7H-01, U4-00), which narrows it down further for the engineer.
What to do with any code
- Write down the code and when it shows: at start-up, on hot water, in the cold.
- Check the pressure gauge and the outdoor unit (see the checks).
- Reset once: off at the isolator for a few minutes, then on.
- If it comes back, book a repair and give the engineer the code, the make and the model.
Samsung, Panasonic, LG, Grant and other makes have their own codes; the manual or the engineer reads them the same way.
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Questions we get asked
What does L9 mean on a Mitsubishi Ecodan?
Low primary circuit flow rate, detected by the flow sensor. Usually low pressure, a blocked magnetic filter, air in the system or a pump fault.
What does 7H mean on a Daikin heat pump?
Abnormal water flow. The same usual causes: pressure, a blocked filter, air or the pump.
What does U4 mean on a Daikin?
The indoor and outdoor units have lost contact: wiring, power to the outdoor unit or a board fault.
Can I clear a heat pump error code myself?
You can reset it once. If it comes back, there's a fault to find.
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