Mitsubishi Electric No code and nothing happeningwhat to check
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.
Take care
What this means
Mitsubishi publish something in their engineer training material that is more useful to an owner than any single code, and it is worth stating in their own terms: with 80% of calls to their customer care team resolved over the phone, experience has generated a list of common issues. The list has four items. Ecodan has been prohibited or stopped on the controller. Power has been switched off to the control board or the immersion heater. The batteries have run out on the wireless controller. And there is low or no flow rate through the Ecodan. That is what four out of five heat pump problems turn out to be, published by the manufacturer, and three of the four take two minutes to check.
Consider what each of them looks like from inside the house, because none announces itself. A system prohibited on the controller is a heat pump that has been told not to run, usually by somebody exploring a menu, and it sits there silent with no fault showing because nothing has failed. Power off to the control board looks identical to a dead heat pump; it is often a tripped breaker or an isolator switched off by somebody working on something else and not switched back.
Flat batteries in a wireless controller are the sneakiest, because the controller looks alive enough to be believed while it has stopped talking to the system, so the house goes cold with nothing on the screen to explain it. Low flow is the one genuine fault in the list, and it usually shows a code. There is a reason this matters beyond saving a call-out. A heat pump that is not running does not necessarily leave you cold, because the backup immersion heater may quietly pick up the load, and then the only symptom is the electricity bill. Working through this list before you conclude the system has failed is not being thorough for its own sake — it is the difference between a two-minute fix and a chargeable visit.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| The system has been prohibited or stopped on the controller | Mitsubishi list this first. The heat pump has been told not to run, so there is no fault and no code — just a system sitting idle while somebody wonders why the house is cold. | Common |
| Power switched off to the control board or immersion heater | A tripped breaker, an isolator switched off during other work, or a spur turned off at the wall. The unit is dead rather than faulty. | Common |
| Flat batteries in the wireless controller | The controller keeps enough life to look normal while losing its link to the system, so the heating stops with nothing obvious on the display. | Common |
| Low or no flow rate through the system | The one real fault on Mitsubishi’s list. This normally does produce a code — on an Ecodan it is usually the low primary flow rate error — and it needs an engineer. | Occasional |
| A schedule or holiday mode suppressing the system | Not on Mitsubishi’s four, but the same class of thing and worth ruling out at the same time. Holiday mode left on after a trip away is a classic. | Occasional |
What to try yourself
Check the controller is not showing the system as prohibited or stopped. This is the first item on Mitsubishi’s own list and it is not a fault state, so nothing will be flagged.
Check the schedule and whether holiday mode is on. A system doing nothing at four in the afternoon because it has been told to may look identical to one that has failed.
Put fresh batteries in the wireless controller. Mitsubishi name this specifically, and a controller with dying batteries stays lit while it stops communicating.
Look at the consumer unit and at any isolator switch near the indoor and outdoor units. A tripped breaker or a switch left off after other work is on Mitsubishi’s list too.
Reset a tripped breaker once, and once only. If it trips again, leave it off and call an electrician or your installer.
Repeatedly resetting a breaker that keeps tripping is the wrong response to an electrical fault. It is protecting the circuit for a reason, and a heat pump is a high-current appliance.If all four check out and the system still will not run, call your installer. You will have already eliminated most of what they would ask you on the phone, which makes the call shorter.
Get an F-Gas certified heat pump engineer to look at your Mitsubishi Electric heat pump
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–£180
Time on site
20 minutes
Nothing for the first three, which is most of them. A visit if it turns out to be flow rate, which is the only genuine fault on the list.
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
- 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
- EFGet it checkedA 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.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
- 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: same brand
Own a Mitsubishi Electric heat pump? Save it and its codes come first next time.
Related guides
Common questions
There is no error code at all. Where do I start?
With Mitsubishi’s own list, because the absence of a code is informative. A system that has failed usually reports something; a system doing nothing quietly has often been told to do nothing. Prohibited on the controller, power off, and flat controller batteries all produce silence rather than an error.
The house is warm but I think something is wrong.
That is worth taking seriously, because a heat pump that has stopped working does not always leave you cold. The backup immersion heater can carry the load and keep the house comfortable while costing several times as much to run, so a bill that has stepped up with no other symptom is a real signal.
Is it worth checking all this before ringing?
Yes, and Mitsubishi’s own figure is the argument for it: four out of five calls to their customer care team are resolved over the phone. Most of those calls are the list above, and a visit for one of them would ordinarily be chargeable.
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
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.