Mitsubishi Electric EF fault codewhat it means and how to fix it
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.
Take care
Which Mitsubishi Electric appliance is showing EF?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
An Ecodan heat pump with a cylinder unit or hydrobox indoors
This page is yours. EF is a non-defined check code caused by noise; Mitsubishi’s remedy is a thirty-second power-down, and the checks around it are the outdoor unit’s power and cable.
Power the Ecodan down for thirty seconds, then check the outdoor unit’s isolator and breaker and the cable run, and call your installer if it returns.
A wall-mounted air conditioner or a ceiling cassette
Mitsubishi publish the same fault for the air-conditioning range, a non-defined code caused by noise with the same thirty-second power-down, but the wiring and isolators to check are the air conditioner’s.
Use the Mitsubishi Electric EF page in the air-conditioning section of this site.
What EF means
EF sits at the end of the E6 to EF block that Mitsubishi’s FTC installation manuals describe in one row as communication failure between the FTC, the flow temperature controller inside your cylinder unit or hydrobox, and the outdoor unit, with three checks: that the outdoor unit has not been turned off, the connecting cable for damage or loose connections, and the outdoor unit service manual. Go to that service manual and EF gets its own definition, the same in the R410A, R32 and R290 Ecodan manuals: "Non defined check code — this code is displayed when non defined check code is received", with two causes, noise on the remote controller’s transmission wire and noise on the wire between the FTC and the outdoor unit, and one action, turn the power off and on again to check, replacing the FTC board or the outdoor controller board only if it appears again.
Mitsubishi’s UK error code lookup says the same for the Ecodan in fewer words: non-defined error code, noise interference in the outdoor unit, power the Ecodan down for thirty seconds and switch back on. So EF is not the outdoor unit reporting a fault; it is the indoor controller receiving something it cannot read, and the published remedy is one an owner can do. The neighbouring letters are the defined communication faults, and they are worth knowing because an EF that keeps returning usually resolves into one of them. E6 is the FTC hearing nothing normal for three minutes, or six minutes after power-up; E8 is the outdoor board hearing nothing for three minutes; E9 is the outdoor board transmitting and getting no answer, which the FTC table lists on its own line as the outdoor unit receiving no signal from the indoor unit.
For all of them Mitsubishi’s first check is that the outdoor unit has not been turned off. An outdoor unit on its own isolator or breaker, switched off by an electrician, tripped, or left off after garden work, cannot answer, and the indoor unit faithfully reports the silence. Their lookup adds the power-up order for the pair: indoor FTC first, then the outdoor unit. One thing that is the same on Mitsubishi’s air conditioners: EF is a non-defined code caused by noise there too, with the same thirty-second remedy, so for once the two product lines agree; the difference is only which wiring and which isolators you are checking.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Electrical noise on the control wiring | Mitsubishi’s two published causes: noise on the remote controller’s transmission wire, or on the cable between the FTC and the outdoor unit. A control cable run alongside mains or near an inverter can be corrupted without any physical damage. | Common |
| Outdoor unit switched off or without power | The FTC manual’s first check for the whole E6 to EF block. An isolator turned off, a tripped breaker or a power cut on the outdoor unit’s own supply looks exactly like a broken cable to the indoor controller. | Common |
| Connecting cable damaged or loose | The FTC manual’s second check. The signal wire between the two units runs outdoors and through walls; rodents, garden tools and disturbed terminals all end here, usually as E6, E8 or E9 rather than EF. | Occasional |
| Failed communication circuit on a board | Mitsubishi’s last resort, reached only if the code returns after a power cycle: either the FTC board or the outdoor controller board. | Rare |
What to try yourself
Switch the Ecodan off at its isolators, wait thirty seconds, and switch it back on. That is Mitsubishi’s published remedy for EF in their UK lookup and the service manual’s action: turn the power off and on again to check. If the indoor and outdoor units have separate isolators, Mitsubishi’s order is indoor FTC first, then the outdoor unit.
If it comes back, find the outdoor unit’s isolator, usually a rotary switch on the wall beside it, and the breaker for it in the consumer unit, and confirm both are on. This is Mitsubishi’s first published check for the E6 to EF block and it costs nothing.
Look along the visible run of cable between the house and the outdoor unit for damage, and at the outdoor unit for signs it has been disturbed. Do not open its electrical cover.
The outdoor unit carries mains and the compressor drive behind its panels. Looking is fine; opening is the installer’s job.If EF persists after one power cycle, or turns into E6, E8 or E9, call your installer and tell them which letters you have seen. Which board or which cable is at fault is decided from the outdoor unit’s own diagnostics.
Get an F-Gas certified heat pump engineer to look at your Mitsubishi Electric EF
We do not pass enquiries to a repair firm, so there is no form here. When you book an F-Gas certified heat pump engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What it costs to fix
Typical repair cost
£0–£500
Time on site
15 minutes
Nothing if the power-down clears it or an isolator was off. A visit to trace and repair the connecting cable is typically £90 to £180. A replacement FTC board or outdoor controller board is the expensive outcome and is usually £300 to £500 fitted.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Mitsubishi Electric fault codes
- J1Get it checkedThe 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.Related: controller and communication
- U1Get it checkedHigh 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.Related: same brand
- L9Get it checkedLow 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.Related: same brand
- No code and nothing happeningGet it checkedMitsubishi 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.Related: same brand
- Outdoor unit failureGet it checkedAny 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.Related: same brand
- L3Get it checkedCirculation 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.Related: same brand
Own a Mitsubishi Electric heat pump? Save it and its codes come first next time.
Related guides
Common questions about Mitsubishi Electric EF
Is this the same EF as on a Mitsubishi air conditioner?
Yes, for once. Mitsubishi’s UK lookup returns two EF rows, one for the air conditioners and one for the Ecodan, and both say non-defined error code, noise interference, power down for thirty seconds; the outdoor service manuals for both product lines define it the same way. What differs is the equipment around it, so if your Mitsubishi blows air, the page in our air-conditioning section walks the right wiring.
The house is still warm. How urgent is it?
Less urgent than it sounds, but do not leave it. If the indoor unit has genuinely lost the outdoor unit, it cannot run the compressor it cannot talk to, so any heat you have is coming from the immersion heater or the booster, and that is the most expensive way to heat a house. A few days is a bill; a few weeks is a shock.
Should I keep switching it off and on?
Once. Mitsubishi’s own instruction is to power off and on again to check, and to replace a board only if the abnormality appears again. If one power cycle does not clear it, the second will not either, and repeated attempts hide the pattern your installer wants to see.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.