Mitsubishi Electric heat pump fault codes

Ecodan is the one heat pump range whose maker prints a grouping rule: any code beginning U, F or A is an outdoor unit failure, in Mitsubishi’s own words. The rest of the table sorts by first letter closely enough to be read the same way, and that tells you where the fault is and therefore who can touch it.

Where the code shows on a Mitsubishi Electric

The first character is the useful part. Mitsubishi publish one rule themselves: codes beginning U, F or A are "Outdoor unit failure", which is the compressor, the inverter, the pressure switches and the refrigerant, and the group no owner and no ordinary electrician should be opening. The rest is read off their table rather than printed as a rule. L codes are what the indoor FTC controller detects: water overheat and freeze protection, low flow, cylinder overheat, its own thermistors, the pressure and flow sensors, boiler-linked faults and DIP switch settings. P1 and P2 are thermistors and P6 is the plate heat exchanger protection. J codes are the wireless controller link, with J0 and J9 the wired FTC ends of it. E codes are wired communications with the main controller and with the outdoor unit. Mitsubishi call these check codes in their service manuals and error codes on the controller; both are their terms for the same thing. One warning before you look anything up: Mitsubishi’s air conditioners share this two-character vocabulary, and the UK error code lookup returns a separate row per product for many codes. Often the fault is the same, U1 being the same high pressure switch on both, but the published checks are for a different machine, so read the Ecodan row. If your Mitsubishi blows air rather than heating water, use the Mitsubishi Electric pages in our air-conditioning section.

How to reset a Mitsubishi Electric

The controller offers "Reset error? No / Yes" on the error screen. On an FTC5 or FTC6 main controller Mitsubishi’s instruction is "Press the F4 (RESET) button, and the F3 (Yes) button to reset the current error"; on the older FTC4 controller it is to hold button E for three seconds. It is worth understanding what that does before using it. Clearing the message does not clear the condition, and a code that returns after a reset is telling you something. Mitsubishi store up to sixteen previous check codes in an error history with the date each occurred, which means a code you cleared last month is still on record for the engineer — so there is no need to leave a fault showing to prove it happened. If the error screen shows a telephone number, that is your installer’s, entered by them at commissioning.

Most common Mitsubishi Electric faults

The Mitsubishi Electric codes people look up most.

Every Mitsubishi Electric fault code

9 published codes. Filtering happens in the page — every one is in the HTML.

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Showing 9 of 9 codes

Every published Mitsubishi Electric fault code with its meaning and severity
Code	What it means	Severity
U1	High pressure: the outdoor unit’s 63H pressure switch has tripped, at 4.15 MPa on R410A and R32 Ecodans and 3.2 MPa on the R290 range. Mitsubishi say it is usually water flow.	Get it checked
L9	Low flow on the primary circuit. Formally an installer job, but the causes are things you can often see — a dirty filter, a closed valve, air after radiator work.	Get it checked
No code and nothing happening	Mitsubishi resolve four in five support calls on the phone, and publish the four common issues behind them. Three take two minutes and none of them is a code.	Get it checked
EF	A code Mitsubishi define as "non defined": noise on the wiring between the controller, the FTC and the outdoor unit. Their published remedy is to power the Ecodan down for thirty seconds.	Get it checked
Outdoor unit failure	Any code starting U, F or A means the outdoor unit; Mitsubishi publish that rule themselves. It is the refrigerant side: F-Gas work on R410A and R32 Ecodans, trained-installer work on the R290 range.	Get it checked
L3	Circulation water temperature overheat protection. The flow rate has probably dropped, and Mitsubishi list three things to check: a water leak, a blocked strainer and the pump.	Get it checked
J1	The wireless receiver cannot hear the wireless room controller. Mitsubishi’s first check is the controller’s batteries, and J1 to J8 all mean the same thing.	Get it checked
P6	Plate heat exchanger protection, usually against freezing. Mitsubishi send the engineer to the L3 flow checks, then to the refrigerant charge, which is F-Gas work on R410A and R32 units.	Get it checked
L4	The cylinder has overheated. Often the immersion heater running when it should not — which is also the fault that quietly doubles your electricity bill.	Get it checked

Mitsubishi Electric models

Codes can differ between generations. Check yours.

Guides that help with Mitsubishi Electric faults

Looking for Mitsubishi Electric’s own support? les.mitsubishielectric.co.uk. We are not affiliated with Mitsubishi Electric.