Mitsubishi Electric heat pump error codes
29 codes that Mitsubishi Electric publishes for its heat pumps, each with what it means, the likely cause, what you can safely check and when to call an installer. Tap your code:
Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work. Anything else is for the heat-pump installer or the maker’s service engineer: in the UK and EU only an F-gas certified technician may open the refrigerant circuit. Codes that need one are marked Installer.
Read this first
Mitsubishi Electric Ecodan heat pumps show a fault on the main controller as a two-character code — L9, E6, P1 — together with the unit and, if your installer registered one, a telephone number to call. The meanings here come from the installation manual of the Ecodan FTC6 controller, written for the installer; what to try first comes from Mitsubishi Electric UK’s heat-pump FAQ for homeowners, which covers the codes owners see most in winter. Models differ: your controller’s manual is the authority.
L9 Low water flow
- What it means
- The flow sensor or flow switch has detected too low a flow rate in the primary (heating) circuit.
- Likely cause
- Mitsubishi Electric’s homeowner FAQ: a water circulation issue, air in the circuit, or a zone valve or pump not being powered. The installer’s checks are water leaks, a blocked strainer and the circulation pump.
- What you can safely check
Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work.
- The homeowner FAQ has a video explaining what L9 means; watch it before calling.
- When to call an installer
- If you cannot correct it, the FAQ says to contact your installer.
Source: Mitsubishi Electric, Mitsubishi Electric UK — Heat Pump FAQ for homeowners: possible error codes during winter Checked 2026-09-29.
E6 E7 E8 EA EB EC ED EF Controller and outdoor unit not communicating
- What it means
- Communication has failed between the FTC controller and the outdoor unit. The manual gives the range E6–EF for this; E9 and EE have rows of their own.
- Likely cause
- The homeowner FAQ says E6 is often down to a power cut or a similar weather event; the installer’s checks are that the outdoor unit has not been switched off and the connecting cable is intact.
- What you can safely check
Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work.
- Has there been a power cut or a storm? The homeowner FAQ has a video showing what to try yourself first.
- When to call an installer
- If that does not clear it, the FAQ says to contact Mitsubishi Electric’s support team; your installer checks the cable and the outdoor unit.
Source: Mitsubishi Electric, Mitsubishi Electric UK — Heat Pump FAQ for homeowners: possible error codes during winter Checked 2026-09-29.
J0 Wireless receiver not communicating
- What it means
- Communication has failed between the FTC controller and the wireless receiver, so the wireless controller is lost.
- Likely cause
- The connection cable between the controller and the receiver, per the installation manual.
- What you can safely check
Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work.
- The homeowner FAQ has a video on what to try at home before contacting your installer when J0 or J1 appears.
- When to call an installer
- Then contact your installer.
Source: Mitsubishi Electric, Mitsubishi Electric UK — Heat Pump FAQ for homeowners: possible error codes during winter Checked 2026-09-29.
J1 J2 J3 J4 J5 J6 J7 J8 Wireless controller not communicating
- What it means
- Communication has failed between the wireless receiver and the wireless remote controller.
- Likely cause
- The installation manual’s checks: a flat battery in the wireless remote controller, and the pairing between receiver and controller.
- What you can safely check
Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work.
- The homeowner FAQ has a video on what to try at home for J0 and J1 before contacting your installer.
- When to call an installer
- If the controller still cannot connect, contact your installer to check the pairing.
Source: Mitsubishi Electric, Mitsubishi Electric UK — Heat Pump FAQ for homeowners: possible error codes during winter Checked 2026-09-29.
P1 Room temperature sensor failure
- What it means
- The installation manual lists P1 as a failure of the room temperature thermistor (TH1).
- Likely cause
- The homeowner FAQ adds that P1 can appear because the controller has been reset, for example by a power cut in a storm.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer The homeowner FAQ suggests getting in touch with your installer to fix it.
Source: Mitsubishi Electric, Mitsubishi Electric UK — Heat Pump FAQ for homeowners: possible error codes during winter Checked 2026-09-29.
L3 Circulation water overheat protection
- What it means
- The water in the primary circuit got too hot and the protection operated.
- Likely cause
- Reduced flow: the manual’s checks are water leaks, a blocked strainer and the circulation pump. It can also show while the primary circuit is being filled.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
L6 Circulation water freeze protection
- What it means
- The water in the primary circuit got close to freezing and the protection operated.
- Likely cause
- Reduced flow, as for L3.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
L4 Hot water tank overheat protection
- What it means
- The water in the hot-water cylinder got too hot and the protection operated.
- Likely cause
- The manual’s check is the immersion heater and its contactor.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer: the immersion heater is wired in.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
L5 Water temperature sensor failure
- What it means
- One of the controller’s water temperature thermistors (THW1, THW2, THW5B, THW6–THW9) has failed.
- Likely cause
- A failed thermistor or its connection.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
L8 Heating operation error
- What it means
- The heating operation did not behave as expected.
- Likely cause
- The manual’s check is for thermistors that have come loose from their pipes.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
LA Pressure sensor failure
- What it means
- The water pressure sensor has failed.
- Likely cause
- Damage or a loose connection on the pressure sensor cable.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
LB High pressure protection
- What it means
- The refrigerant high-pressure protection operated.
- Likely cause
- Reduced flow in the heating circuit, a clogged plate heat exchanger, or an outdoor unit failure.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
LF Flow sensor failure
- What it means
- The flow sensor has failed.
- Likely cause
- Damage or a loose connection on the flow sensor cable.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
P6 Plate heat exchanger anti-freeze protection
- What it means
- The anti-freeze protection of the plate heat exchanger operated.
- Likely cause
- Reduced flow (as for L3), or the wrong amount of refrigerant.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer: a refrigerant check is F-gas certified work.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
E9 Outdoor unit receives no signal
- What it means
- The outdoor unit is receiving no signal from the indoor unit.
- Likely cause
- The manual’s checks: both units switched on, and the connecting cable intact.
- What you can safely check
Nothing for the owner to check: this one is for an installer.
- When to call an installer
- Installer Contact your installer.
Source: Mitsubishi Electric, Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
A code that is not listed here
A code starting U, F or A on an Ecodan is an outdoor-unit failure: the FTC6 manual sends the installer to the outdoor unit’s service manual. For any other code not listed here, contact your installer, or Mitsubishi Electric UK’s support team through them.
We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.
Related pages
Source
Every code on this page comes from these pages, published by Mitsubishi Electric and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.
- Mitsubishi Electric: Ecodan FTC6 PAC-IF07(1-3)B-E Installation Manual (BH79D843H06): 6.2 Self-check, error codes Checked 2026-09-29.
- Mitsubishi Electric: Mitsubishi Electric UK — Heat Pump FAQ for homeowners: possible error codes during winter Checked 2026-09-29.