LL on a Mitsubishi Electric heat pump: Setting errors of DIP switches on FTC4 control board (boiler, 2-zone, multiple outdoor units)
Short answer
On a Mitsubishi Electric heat pump, LL means: Setting errors of DIP switches on FTC4 control board (boiler, 2-zone, multiple outdoor units). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 5 sources
What it means
On the Ecodan
The manuals for this range word it in different ways:
- Setting errors of DIP switches on FTC4 control board (boiler, 2-zone, multiple outdoor units).
- Setting errors of DIP switches on FTC control board (boiler / 2-zone).
Part involved: FTC DIP switches.
When it shows: Incompatible DIP switch combination detected.
Likely causes:
- Incorrect setting of DIP switches (commissioning error).
On the Ecodan Hydrodan
The manual says: Setting errors of DIP switches on FTC control board (boiler / 2-zone).
Part involved: FTC DIP switches.
When it shows: Incompatible DIP switch combination detected.
Likely causes:
- Incorrect setting of DIP switches (commissioning error).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Not stated as auto-resetting; code remains until reset.
Manual reset: Installation manuals: press F4 (RESET) then F3 (Yes) on the main remote controller (older controllers: hold button E for 3 s); 'To cancel error codes please switch system off'. Fix the cause first.
What you can check
- Note the code, unit and ref. address shown on the main remote controller and contact your installer (Mitsubishi user manuals: 'Make a note of the error code number and contact installer'). Check the heat pump breaker/isolator at the consumer unit is on and read the primary system pressure gauge (if fitted) so you can report it. A single reset from the main remote controller (RESET, then Yes) may be tried; if the code returns, do not keep resetting. Do not open the outdoor unit, cylinder/hydrobox or any casing.
What the engineer will check
On the Ecodan
- Boiler: DIP SW1-1 ON (with boiler) and SW2-6 ON (with mixing tank); 2-zone: SW2-7 ON and SW2-6 ON; multiple outdoor units control: SW1-3 ON on the slave unit that runs DHW.
- Boiler: DIP SW1-1 ON (with boiler) and SW2-6 ON (with mixing tank); 2-zone: SW2-7 ON (2-zone) and SW2-6 ON (with mixing tank).
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
On the Ecodan Hydrodan
- Boiler: DIP SW1-1 ON (with boiler) and SW2-6 ON (with mixing tank); 2-zone: SW2-7 ON (2-zone) and SW2-6 ON (with mixing tank).
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (controls / wiring).
What you might notice
What owners and engineers report
2 owner and engineer reports mention this.
- Heat pump will not start on the Ecodan: 2 reports
Sources
- Ecodan EHSC-VM2B / EHPX-VM2B Service Manual ↗ · OCH532A · page 55 (10-4 Self-diagnosis and action) · Reviewed 23 September 2026
- Ecodan FTC5 - EHPT20X-MHCW, EHST20(D)(C)-MHCW Cylinder Service Manual (OCH570C) ↗ · OCH570C · page 66 (10-4 Self-diagnosis and action) · Reviewed 23 September 2026
- Ecodan EHPT20X-MHEDWR1 Service Manual (OCH714E) ↗ · OCH714E · page 58 (10-4 Self-diagnosis and action) · Reviewed 23 September 2026
- Ecodan EHPT20X-MEHEW Service Manual (OCH814A) ↗ · OCH814A · page 62 (10-4 Self-diagnosis and action) · Reviewed 23 September 2026
- Ecodan Hydrodan EHWT17D-MHEDW Installation Manual RK79D203K04 ↗ · RK79D203K04 · page 48 (PDF p.49, Error Codes (FTC)) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026