Mitsubishi Electric EF fault codewhat it means and how to fix it
A non-defined error that Mitsubishi attribute to noise interference, with a published owner remedy: power down for thirty seconds.
Before you start
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.
A wall-mounted air conditioner or a ceiling cassette
This page is yours. EF is a non-defined error Mitsubishi attribute to noise, with a published owner remedy.
Power the system down for thirty seconds, switch it back on, and treat a repeat as a wiring question for an engineer.
An Ecodan heat pump with radiators, underfloor heating or a hot water cylinder
Same fault and the same thirty-second power-down, but Mitsubishi publish a separate Ecodan row and the checks around it, the outdoor isolator and the connecting cable, belong to that appliance.
Use the Mitsubishi Electric EF page in the heat-pumps section of this site instead.
What EF means
EF is unusual in this whole category and that is why it earns a page. Mitsubishi publish it as a non-defined error code, give the cause as noise interference, and give the remedy as powering the system down for thirty seconds and then switching it back on. That is an owner action, published by the manufacturer, on a brand where almost every other check procedure involves DIP switches inside electrical enclosures or a service menu behind a password.
If you have this code, the thing to do is the thing everybody tries anyway — and here it is actually correct. Noise interference means electrical noise on the control wiring rather than anything audible. The indoor and outdoor units talk to each other over a low-voltage signal, and that signal shares a world with mains cables, motors, inverters, fluorescent lighting and everything else in a building. Occasionally something corrupts a message badly enough that the receiving end cannot interpret it, and rather than guessing, the system raises a fault it cannot classify. Nothing has broken. The system has simply received something it did not understand and stopped rather than act on it.
Two things follow. First, a single EF that clears on a power cycle and never returns is exactly what a transient looks like, and chasing it further is a waste of money. Second, an EF that keeps coming back is telling you something real about the installation — typically that the control cable is running alongside a mains cable it should not be, that a connection has degraded, or that new equipment has been installed nearby. That is a wiring investigation rather than a component replacement, and it is worth framing it that way when you call, because otherwise the temptation is to change boards. Worth noting the company this code keeps. Mitsubishi publish at least two other codes that are not faults at all: one whose stated cause is simply that everything is normal, and one that means a test-operation switch has been left switched on. A code is not automatically a failure on this manufacturer.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Electrical noise on the control wiring | Mitsubishi’s published cause. Something corrupted a message between units badly enough that it could not be interpreted, so the system raised an unclassified fault. | Common |
| Control cable routed alongside mains cabling | The classic installation cause of recurring noise. A single event is a transient; a repeating one usually means the cable is picking up interference by proximity. | Occasional |
| A degraded or loose connection | A poor termination makes the signal more vulnerable to interference that clean wiring would shrug off. Often appears after other work. | Occasional |
| New equipment installed nearby | Inverters, motors and some lighting all generate interference. An EF that starts appearing after something else was fitted is worth connecting to it. | Occasional |
What to try yourself
Power the system down for thirty seconds and switch it back on. This is Mitsubishi’s own published remedy for this code, not a generic suggestion.
Use the isolator or the breaker rather than the remote. Standby is not off, and the remote does not remove power from the control electronics.
Run the system normally afterwards and see whether it returns. A one-off that never comes back was a transient and needs nothing further.
If it recurs, note when. A pattern that follows another appliance switching on points at interference from that appliance.
Think about whether anything has been installed or rewired recently, indoors or out, near the route the control cable takes.
For a recurring EF, ask for the control wiring and its routing to be investigated rather than for boards to be replaced.
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–£220
Time on site
20 minutes
Nothing for a one-off, which is most of them. An engineer visit if it recurs, and that should be a wiring investigation rather than parts.
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
- PAGet it checkedA drain fault. Mitsubishi tell their own engineers not to assume the pump has failed — the usual cause is a blockage backing the water up.Related: same brand
- U1Get it checkedU1 is a high-pressure fault on a Mitsubishi air conditioner and on an Ecodan alike. The fault is the same; the checks depend on which appliance you have.Related: same brand
- 2503Get it checkedA drain sensor fault, which is the version where the tray is clean. Mitsubishi note the indoor unit may have a float switch instead of a sensor.Related: same brand
Own a Mitsubishi Electric air conditioner? Save it and its codes come first next time.
Related guides
Common questions about Mitsubishi Electric EF
Is thirty seconds important, or can I just flick it off and on?
Thirty seconds is the published figure, so use it. Control electronics hold enough charge to keep running briefly after the supply is removed, and a quick flick may not fully reset them — which is how people conclude a valid reset procedure does not work.
It has come back three times now.
Then treat it as an installation question rather than a fault to keep clearing. A repeating noise error usually means the control cable is picking up interference — often from running too close to mains cabling — or that a connection has degraded. That is a wiring investigation, not a board replacement.
What does non-defined error actually mean?
That the system knows something went wrong but could not classify it. Rather than guess at a specific fault, it reports that it received something it could not interpret. It is an honest answer from the machine, and it is why the remedy is a reset rather than a repair.
Should I worry that a code appeared at all?
Not on this manufacturer, on the strength of this code alone. Mitsubishi publish at least two codes that are explicitly not faults — one whose stated cause is that everything is normal, and one meaning a test switch was left on. A code here is information, not automatically a failure.
I have an Ecodan heat pump showing EF, not an air conditioner.
Same fault and same remedy. Mitsubishi’s lookup carries an Ecodan row for EF with the same non-defined error, noise interference as the cause and the same thirty-second power-down, so nothing about the code itself changes. What changes is the machine around it: an Ecodan’s indoor controller and outdoor unit sit on separate supplies, and the Ecodan manual puts EF in its communication block, so the checks there start with the outdoor unit’s isolator and the connecting cable before the power cycle. The Mitsubishi Electric EF page in our heat-pumps section is written for it.
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 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.