In case of breakage, the Mitsubishi thermostat will show you different fault codes. You could use the tables below to understand the cause of the problem. Each table refers to 4 models of Mitsubishi thermostats. With the help of this information, you can determine the cause of failure and to fix it. Often the problem can be solved without repairman.
Mitsubishi MD315301 Thermostat Error Codes
| FAULT CODE | DESCRIPTION |
|---|---|
| F3 | Low pressure switch failure – check connection on the board and continuity of switch |
| F5 | High pressure switch failure – check connection onto board and continuity of switch |
| F9 | Both pressure switch contacts are open at the same time – check connection onto board and continuity of switch and for a potential board failure |
| EA | Mis-wiring fault between FTC and Ecodan – check S1 ,S2,S3 also check voltages and comms |
| EB | Mis-wiring fault between FTC and Ecodan – Check S1 ,S2,S3 also check voltages and comms |
| EC | Unit cannot finish start up process – generally caused by a comms fault |
| U1 | Ecodan high pressure fault – mainly caused by incorrect water flow rates – check with flow setter |
| U2 | Ecodan high compressor discharge temperature – mainly caused by refrigerant shortage or dirty condenser |
| U3 | Ecodan discharge thermistor problem – mainly caused by TH4 discharge thermistor – open/close circuit |
| U4 | Open or close circuit Ecodan thermistors (TH3, TH32, TH33, TH6, TH7, TH8) – open or close circuit or disconnected from main board |
| U5 | Inverter heat sink overheat protection (W50 and W85 models 77°C, HW140 model 95°C – reduced air flow through Ecodan – faulty fan motor |
| U6 | Inverter/Compressor over current – system indicates possible I PM error |
| U8 | Ecodan fan motor problem – mainly caused by DC fan motor being disconnected, connected or obstructed with the power on or possible main board fault |
| U9 | Over voltage or under voltage – mainly caused by either CN2 or CN5 loose or disconnected or decrease of mains power supply |
| UD | Overheat protection TH3 s 70°C or 63 HS s 70°C saturation temperature |
| UF | Compressor over current/Compressor lock – occurs within 30 seconds of compressor start |
| UH | Abnormal running current – < 1A or > 40A detected during operation – check CN5 connections |
| UL | Open circuit (63L) |
| UP | Over current detected after 30 seconds of operation – do an inverter test to determine outputs balanced |
| EO | Transmitting Error PAR W21 – check refrigerant address on SW1 of Ecodan |
Mitsubishi SMD315301 Thermostat Error Codes
| FAULT CODE | 1 DESCRIPTION |
|---|---|
| E1 | Faulty controller |
| E3 | Transmitting Error (PAR W21) – check refrigerant address on SW1 of Ecodan |
| E4 | Receiving Error (PAR W21) – check refrigerant address of SW1 on Ecodan |
| E5 | Receiving Error (PAR W21) – check refrigerant address of SW1 on Ecodan |
| E6 | Indoor/Outdoor communication error – mainly due to Ecodan being powered up before FTC(2) |
| E8 | Indoor/Outdoor communication error – mainly due to Ecodan being powered up before FTC(2) |
| E9 | Indoor/Outdoor communication error – mainly due to Ecodan being powered up before FTC(2) |
| EF | Non-defined error code – noise interference – power down Ecodan for 30 seconds then switch back on |
| ED | Serial communication fault between Ecodan main board and Ecodan inverter board – mainly due to loose CN2 or CN5 cable |
| P1 | Flow temp sensor fault – TH1 not connected, short or open circuit |
| P6 | Over heating at heat exchanger – lack of water flow, air in the system, flow rate incorrectly set, blockage or pump problem |
| P8 | No temp change at plate heat exchanger – problem with flow rate (too high) – incorrect sizing of system |
| P9 | TH5 Fault – TH5 not connected, short or open circuit, FTC not configured for heating only |
| PE | Inlet water temp fault – TH32 is below 10°C whilst compressor is in operation – possible thermistor out of range, short of gas, incorrect sizing of radiator or problem in the water circuit (blockage, pump failure etc) |
Mitsubishi Mr Slim Thermostat Error Codes
| Check code | Diagnosis | Cause | Check points |
|---|---|---|---|
| EO | Signal transmitting/receiving error (Indoor controller does not respond to remote controller signal.) | 1) Bad contact of transmission wire | 1) Check the transmission wire. |
| 2) Signal transmitting/receiving circuit is abnormal. | 2) Check with another remote controller. If “EO” is still indicated, replace the indoor controller board. | ||
| If other check code appears, replace the original remote controller. | |||
| P1 | Abnormality of room temperature thermistor | 1) Bad contact of thermistor | 1) Check the thermistor. |
| 2) Damaged thermistor | 2) Measure the resistance of the thermistor. Normal resistance should be as follows. 32°F–15K2 86° F 4.3kfi 50°F 9.6kni04°F 3.0kQ 68°F 6.3kH | ||
| P2 | Abnormality of indoor coil thermistor | If the resistance is normal, replace the indoor controller board. | |
| P3 | Signal transmission error (Remote controller does not respond to indoor controller signal.) | 1) Bad contact of transmission wire | 1) Check the transmission wire. |
| 2) Signal transmitting/receiving circuit is abnormal. | 2) Check with another remote controller. If “P3″ is still indicated, replace the indoor board. If other check code appears, replace the original remote controller. | ||
| 3) Wrong operation due to noise wave emitted by other appliances | 3) Short-circuit between | ||
| • Second unit in twin control | |||
| • Second and third units in triple control | |||
| • Sub units in group control | |||
| P4 | Abnormality of drain sensor | 1) Bad contact of transmission wire | 1) Check the connector. |
| 2) Damaged thermistor | 2) Measure the resistance of the thermistor As for the normal resistance, refer to the case of P1. | ||
| If the resistance is normal, replace the indoor controller board. | |||
| P5 | Malfunction of drain pump | 1) Malfunction of drain pump | 1) Check the drain pump. |
| 2) Damaged drain sensor | 2) • Check the drain sensor. | ||
| • Check the drain sensor heater. | |||
| If the resistance is normal, replace the indoor controller board. | |||
| P6 | Coil frost protection is working. | 1) Short cycle of air cycle | 1) Clear obstructions from the air cycle. |
| 2) Dirty air filter | 2) Clean the air filter | ||
| 3) Damaged fan | 3) Check the fan. | ||
| 4) Abnormal refrigerant | 4) Check the refrigerant temperature. | ||
| P7 | System error | 1) Wrong address-setting | 1) Check the address-setting. |
| 2) Signal transmitting/receiving circuit of remote controller is abnormal. | 2) Check with another remote controller. If check code other than “P7″ appears, replace the original remote controller. | ||
| 3) Wrong SW6-setting | 3) Check SW6 setting. |
Mitsubishi P-SERIES Thermostat Error Codes
| Blinking LED | Diagnosis | Cause | Check point |
|---|---|---|---|
| LD1 | Reversed phase | This model does not have this function. | No need to be checked. |
| LD2 | Open phase | This model does not have this function. | No need to be checked. |
| LD3 | Outdoor coil thermistor is abnormal. (Open circuit or short circuit) | • Outdoor coil thermistor is broken. | • Measure the resistance of the thermistor. |
| • Thermistor was connected incorrectly. | • Check the thermistor. If normal, replace the out- door controller board. | ||
| LD4 | High pressure switch (63H2) function | • 63H2 was badly connected. | • Check 63H2 and the outdoor fan motor. |
| • 63H2 was working. | • Check if refrigerant supply is low. | ||
| • Check if air cycle is short-cycled. | |||
| LD5 | Thermal relay function | This model does not have this function. | No need to be checked. |
| LD6 | Thermal switch (26C) function. | • 26C was connected incorrectly. | • Check 26C. |
| • 26C is working. | • Check if refrigerant supply is low. | ||
| • Check if the capillary tube is clogged. | |||
| LD7 | Over heat protection | • The thermistor is broken. | • Measure the resistance of the thermistor. |
| • Coil temperature is over 153°F. | • Check the outdoor fan motor. | ||
| • Check if air cycle is short-cycled. | |||
| LD8 | Input circuit of outdoor controller board is abnormal. | • Pulse input is abnormal. | • Replace the outdoor controller board. |