Baxi
The Baxi HP40/50 is an R32 monobloc air source heat pump range with outputs from 4kW to 13kW, featuring a 65 degree Celsius maximum flow temperature and MCS certification.
The Baxi HP40/50 is a monobloc air source heat pump range designed for domestic heating and hot water applications. Utilizing R32 refrigerant, these DC inverter units offer nominal capacities from 4kW to 13kW. The HP50 model features a 4kW output, a maximum flow temperature of 65°C, and is MCS certified for Boiler Upgrade Scheme eligibility. This technical guide provides engineers with essential specifications, installation clearances, and comprehensive fault code diagnostic data for the HP40/50 series.
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Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
The Baxi HP40/50 series represents a versatile monobloc solution for UK residential decarbonisation. These units are engineered as DC inverter-driven systems, ensuring modulated output to match the building's heat loss. The range includes single-phase models from 4kW to 13kW and three-phase variants at 11kW and 13kW, catering to a wide variety of property sizes. From a technical perspective, the HP40/50 utilizes R32 refrigerant, which has a Global Warming Potential (GWP) of 675. The 4kW to 8kW models carry a 1.4kg charge, while the larger 11kW to 13kW units require 1.75kg. Electrical requirements are specific to the output: the 4kW to 8kW units require a 25A MCB, whereas the 11kW to 13kW single-phase models necessitate a 35A supply. For three-phase installations, the 11kW and 13kW models operate on a 14A supply.
Hydraulic performance is a core strength of the HP40/50. The units can achieve a maximum flow temperature of 65°C, making them suitable for both underfloor heating and correctly sized radiator circuits. The system operates within a broad ambient temperature range, functioning down to -25°C. For installation, engineers must ensure a minimum water flow rate of 6.67 litres per minute and account for a maximum operating pressure of 3 bar. The outdoor unit for the HP50 model measures 792mm in height, 1295mm in width, and 429mm in depth, with a net weight of 98kg.
Installation clearances are critical for maintaining airflow and service access. The manufacturer specifies a minimum of 300mm at the sides and rear, 500mm above the unit, and a front clearance of 1000mm for 4kW and 5kW models, increasing to 1500mm for larger outputs. The unit is compatible with the Assure ASHP Cylinder and requires a buffer tank for most configurations to ensure sufficient system volume. Maintenance and diagnostics are facilitated by the wired controller. Common fault codes include E0 and E8, which typically indicate water flow issues, often caused by air in the system or a dirty filter. Protection codes like P5 monitor the temperature differential between the inlet and outlet, ensuring the heat exchanger operates within safe parameters. Annual servicing is mandatory to maintain the warranty, including checks of the water pressure, filter cleaning, and expansion vessel integrity.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/heat-pumps/baxi/hp40-50-11-1phmb#fault-e0 to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| E0Lockout | Water flow fault (after 3 times E8) Show causes & actionsThe unit has detected a persistent water flow issue after multiple attempts. Likely causes
Engineer action 1) The wire circuit has short-circuited or is open. Reconnect the wire correctly. 2) Water flow rate is too low. 3) Water flow switch is failed, switch is open or closed continuously, change the water flow switch. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E2 | Communication fault between controller and hydraulic module Show causes & actionsLoss of communication between the wired controller and the internal hydraulic module. Likely causes
Engineer action 1) Wire does not connect between wired controller and unit. Connect the wire. 2) Communication wire sequence is not correct. Reconnect the wire in the correct sequence. 3) There is a high magnetic field or high power interfere. Add a barrier to protect the unit or move the unit to a different location. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E3 | Final outlet water temp.sensor (T1) fault Show causes & actionsMalfunction of the T1 temperature sensor at the final water outlet. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The T1 sensor connector is loose. Reconnect it. 3) The T1 sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 4) The T1 sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E4 | water tank temp. sensor (T5) fault Show causes & actionsMalfunction of the domestic hot water tank temperature sensor. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The T5 sensor connector is loose. Reconnect it. 3) The T5 sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 4) The T5 sensor has failed, replace with a new sensor. 5) To close the domestic water heating when T5 sensor is not connected to the system, refer to 10.5.1 'DHW MODE SETTING'. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E7 | Buffer tank up temp. sensor (Tbt1) fault Show causes & actionsMalfunction of the upper buffer tank temperature sensor. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The Tbt1 sensor connector is loose, reconnect it. 3) The Tbt1 sensor connector is wet or has water in, remove the water, dry the connector. Add waterproof adhesive. 4) The Tbt1 sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E8 | Water flow failure Show causes & actionsThe unit has detected insufficient water flow through the system. Likely causes
User action Refer to 9.5 Filling water. Engineer action 1) Check that all shut off valves of the water circuit are completely open. 2) Check if the water filter needs cleaning. 3) Refer to 9.5 Filling water. 4) Make sure there is no air in the system (purge air). 5) Check the water pressure. The water pressure must be >1 bar (0.1 MPa). 6) Check that the pump speed setting is on the highest speed. 7) Make sure that the expansion vessel is not broken. 8) Check that the resistance in the water circuit is not too high for the pump (refer to 10.4 The circulation pump). 9) If this error occurs at defrost operation, make sure that the backup heater power supply is wired correctly. 10) Check that the pump fuse and PCB fuse are not blown. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| Eb | Solar temp.sensor (Tsolar) fault Show causes & actionsMalfunction of the solar temperature sensor. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The Tsolar sensor connector is loose, reconnect it. 3) The Tsolar sensor connector is wet or has water in, remove the water, dry the connector. Add waterproof adhesive. 4) The Tsolar sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| Ec | Buffer tank low temp. sensor(Tbt2) fault Show causes & actionsMalfunction of the lower buffer tank temperature sensor. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The Tbt12 sensor connector is loose, reconnect it. 3) The Tbt2 sensor connector is wet or has water in, remove the water, dry the connector. Add waterproof adhesive. 4) The Tbt2 sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| Ed | Inlet water temp. sensor (Tw_in) malfunction Show causes & actionsMalfunction of the inlet water temperature sensor. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The Tw_in sensor connector is loose. Reconnect it. 3) The Tw_in sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 4) The Tw_in sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| EE | Hydraulic module EEprom failure Show causes & actionsInternal memory error on the hydraulic module control board. Likely causes
Engineer action 1) The EEprom parameter is error, rewrite the EEprom data. 2) EEprom chip part is broken, replace with a new EEprom chip part. 3) Main control board of hydraulic module is broken, replace with a new PCB. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H0 | Communication fault between main board PCB B and main control board of hydraulic module Show causes & actionsCommunication failure between the heat pump system board and the hydraulic module board. Likely causes
Engineer action 1) Wire doesn’t connect between main control board PCB B and main control board of hydraulic module. Connect the wire. 2) Communication wire sequence is not correct. Reconnect the wire in the correct sequence. 3) There is a high magnetic field or high power interfere. Add a barrier to protect the unit or move the unit to a different location. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H2 | Refrigerant liquid temp. sensor (T2) fault Show causes & actionsMalfunction of the refrigerant liquid side temperature sensor. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The T2 sensor connector is loose. Reconnect it. 3) The T2 sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 4) The T2 sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H3 | Refrigerant gas temp. sensor (T2B) fault Show causes & actionsMalfunction of the refrigerant gas side temperature sensor. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The T2B sensor connector is loose. Reconnect it. 3) The T2B sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 4) The T2B sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H5 | Room temp. sensor (Ta) fault Show causes & actionsMalfunction of the room temperature sensor. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The Ta sensor is in the interface. 3) The Ta sensor has failed, replace with a new sensor or change a new interface, or reset the Ta, connect a new Ta from the hydraulic module PCB. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H9 | Outlet water for zone 2 temp. sensor (Tw2) fault Show causes & actionsMalfunction of the temperature sensor for the zone 2 water outlet. Likely causes
Engineer action 1) Check the resistance of the sensor. 2) The Tw2 sensor connector is loose. Reconnect it. 3) The Tw2 sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 4) The Tw2 sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| HA | Outlet water temp. sensor (Tw_out) fault Show causes & actionsMalfunction of the outlet water temperature sensor. Likely causes
Engineer action 1) The TW_out sensor connector is loose. Reconnect it. 2) The TW_out sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 3) The TW_out sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| HbLockout | Three times “PP” protection and Tw_out < 7°C Show causes & actionsPersistent low temperature protection at the water outlet. Likely causes
Engineer action Refer to 'PP'. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| Hd | Communication fault between hydraulic module parallel Show causes & actionsCommunication failure in a cascaded system between multiple units. Likely causes
Engineer action 1) Check signal wires are well connected. 2) Ensure only one wired controller is connected to the master unit. 3) Ensure power-on interval between units is less than 2 minutes. 4) Check for duplicate addresses using SW2 button; clear addresses if necessary. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| HE | Communication error between main board and thermostat transfer board Show causes & actionsLoss of communication with the optional thermostat transfer board. Likely causes
Engineer action If thermostat transfer board is needed, please connect it to main board and make sure the communication wire is connected correctly and there is no strong electricity or strong magnetic interference. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| P5 | (Tw_out - Twin) value too big protection Show causes & actionsExcessive temperature difference between water inlet and outlet. Likely causes
Engineer action 1) Check that all shut off valves are completely open. 2) Check if the water filter needs cleaning. 3) Refer to '9.5 Filling water'. 4) Make sure there is no air in the system. 5) Check the water pressure (>1 bar). 6) Check that the pump speed setting is on the highest setting. 7) Check that resistance in the water circuit is not too high. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| Pb | Anti freeze mode Show causes & actionsThe unit has entered anti-freeze protection mode. Likely causes
Engineer action Unit will return to the normal operation automatically. Reset procedure Automatic reset. | Details |
| PP | Tw_out - Tw_in unusual protection Show causes & actionsAbnormal temperature differential between inlet and outlet sensors. Likely causes
Engineer action 1) Check the resistance of the two sensors. 2) Check the two sensors location. 3) The water inlet/outlet sensor wire connector is loose, reconnect it. 4) The water inlet/outlet (TW_in/TW_out) sensor is broken, replace with a new sensor. 5) Four-way valve is blocked. Restart the unit again. 6) Four-way valve is broken, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E1 | Phase loss or neutral wire and live wire are connected reversely Show causes & actionsElectrical supply error (3-phase units only). Likely causes
Engineer action 1) Check the power supply cables are firmly connected, avoid phase loss. 2) Check whether the sequence of neutral wire and live wire are connected reversely. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E5 | The condenser outlet refrigerant temperature sensor (T3) error. Show causes & actionsMalfunction of the T3 refrigerant temperature sensor. Likely causes
Engineer action 1) The T3 sensor connector is loose. Reconnect it. 2) The T3 sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 3) The T3 sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E6 | The ambient temperature sensor (T4) error. Show causes & actionsMalfunction of the outdoor ambient temperature sensor. Likely causes
Engineer action 1) The T4 sensor connector is loose. Reconnect it. 2) The T4 sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 3) The T4 sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| E9 | Suction temperature sensor (Th) error Show causes & actionsMalfunction of the compressor suction temperature sensor. Likely causes
Engineer action 1) The Th sensor connector is loose. Reconnect it. 2) The Th sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 3) The Th sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| EA | Discharge temperature sensor (Tp) error Show causes & actionsMalfunction of the compressor discharge temperature sensor. Likely causes
Engineer action 1) The Tp sensor connector is loose. Reconnect it. 2) The Tp sensor connector is wet or has water in. Remove the water, dry the connector. Add waterproof adhesive. 3) The Tp sensor has failed, replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H1 | Communication error between inverter module PCB A and main control board PCB B Show causes & actionsInternal communication failure between control boards. Likely causes
Engineer action 1) Check if there is power connected to the PCB and driven board. 2) Check the wire connection between inverter module PCB and main control board PCB. 3) Replace a new main PCB and driven board one by one. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H4Lockout | Three times P6 (L0/L1) protect Show causes & actionsRepeated module or voltage protection faults. Likely causes
Engineer action See L0 and L1 for fault handling methods. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H6 | The DC fan failure Show causes & actionsMalfunction of the outdoor unit fan motor. Likely causes
Engineer action 1) Change the unit direction or make shelter to avoid typhoon. 2) fan motor is broken, replace with a new fan motor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H7 | Voltage protection Show causes & actionsSupply voltage is outside of the allowable range. Likely causes
Engineer action 1) Check whether the power supply input is in the available range. 2) Power off and power on several times rapidly. Keep the unit power off for more than 3 minutes then power on. 3) The circuit defect part of Main control board is defective. Replace with a new Main PCB. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| H8 | Pressure sensor failure Show causes & actionsMalfunction of the refrigerant pressure sensor. Likely causes
Engineer action 1) Pressure sensor connector is loose, reconnect it. 2) Pressure sensor failure. Replace with a new sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| HF | Inverter module board EE prom failure Show causes & actionsMemory error on the inverter module board. Likely causes
Engineer action 1) The EE prom parameter is erroneous, rewrite the EE prom data. 2) EE prom chip part is broken, replace with a new EE prom chip part. 3) Inverter module board is broken, replace with a new PCB. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| HHLockout | H6 displayed 10 times in 2 hours Show causes & actionsPersistent fan failure detected. Likely causes
Engineer action Refer to H6. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| HPLockout | Low pressure protection in cooling Pe < 0.6 occurred 3 times in an hour. Show causes & actionsRepeated low refrigerant pressure detected during cooling mode. Likely causes
Engineer action Refer to P0. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| P0 | Low pressure switch protection Show causes & actionsRefrigerant pressure has dropped below the safety threshold. Likely causes
Engineer action 1) Charge the refrigerant in right volume. 2) Clean the outdoor heat exchanger or remove the obstruction. 3) Increase the water flow. 4) Tap the valve body and plug in/plug off the connector for several times. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| P1 | High pressure switch protection Show causes & actionsRefrigerant pressure has exceeded the safety threshold. Likely causes
Engineer action 1) Release the air from the water system. 2) Charge the water to 1.5-2 bar. 3) Recharge the refrigerant in right volume. 4) Tap the valve body and plug in/plug off the connector. 5) Check heat exchanger size and cleanliness. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| P3 | Compressor overcurrent protection. Show causes & actionsCompressor is drawing excessive electrical current. Likely causes
Engineer action 1) Refer to P1. 2) Increase the power voltage to the required range. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| P4 | High discharge temperature protection. Show causes & actionsCompressor discharge temperature is too high. Likely causes
Engineer action 1) Refer to P1. 2) Reconnect loose sensors. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| Pd | High temperature protection of refrigerant outlet temp of condenser. Show causes & actionsCondenser outlet temperature is too high. Likely causes
Engineer action 1) Remove heat exchanger cover. 2) Clean the heat exchanger or remove obstruction. 3) Ensure enough space around the unit. 4) Replace fan motor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| C7 | Transducer module temperature too high protection. Show causes & actionsThe power module temperature has exceeded safety limits. Likely causes
Engineer action 1) Increase power voltage. 2) Increase space between units. 3) Clean heat exchanger. 4) Replace fan motor. 5) Release air and reselect pump. 6) Reconnect or replace water outlet temp. sensor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| F1 | Low DC generatrix voltage protection Show causes & actionsInternal DC bus voltage is too low. Likely causes
Engineer action 1) Check power supply. 2) Check voltage PN; replace inverter board if damaged. 3) Check rectifier bridge. 4) Check main board. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| bH | PED PCB failure Show causes & actionsMalfunction of the PED safety board. Likely causes
Engineer action 1) Power off for 5 minutes and restart. 2) Replace PED safety plate. 3) Replace IPM module board. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| L0 | Module protection Show causes & actionsGeneral power module protection fault. Likely causes
Engineer action Check the Heat pump system pressure and phase resistance of compressor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| L1 | DC generatrix low voltage protection Show causes & actionsInternal DC bus voltage low. Likely causes
Engineer action Check the Heat pump system pressure and phase resistance of compressor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| L2 | DC generatrix high voltage protection Show causes & actionsInternal DC bus voltage high. Likely causes
Engineer action Check the Heat pump system pressure and phase resistance of compressor. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| L4 | MCE malfunction Show causes & actionsMotor control error detected. Likely causes
Engineer action 1) Check the U, V, W power line connection sequence. 2) Check the L1, L2, L3 power line connection. 3) Check the inverter board. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| L5 | Zero speed protection Show causes & actionsCompressor failed to start or maintain speed. Likely causes
Engineer action Check the inverter board. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| L8 | Speed difference > 15Hz protection between the front and the back clock Show causes & actionsInternal timing or speed synchronization error. Likely causes
Engineer action Check the inverter board. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
| L9 | Speed difference > 15Hz protection between the real and the setting speed Show causes & actionsCompressor speed deviation error. Likely causes
Engineer action Check the inverter board. Reset procedure Apply the relevant corrective action, then reset the safety device by turning the unit OFF and back ON. | Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
Engineer: 1) The wire circuit has short-circuited or is open. Reconnect the wire correctly. 2) Water flow rate is too low. 3) Water flow switch is failed, switch is open or closed continuously, change the water flow switch.
Triggered by fault code E0.
Engineer: Refer to 'PP'.
Triggered by fault code Hb.
Engineer: See L0 and L1 for fault handling methods.
Triggered by fault code H4.
Common questions from engineers and homeowners about the Baxi HP40/50-11-1PHMB.
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Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 30 April 2026.
Engineer: Refer to H6.
Triggered by fault code HH.
Engineer: Refer to P0.
Triggered by fault code HP.