Ecodan L9: three different flow faults share one code
The FTC shows L9 for the heat source side, Zone1, and Zone2 alike. Request code 569 separates them, and the flow figure to check is not the 5 litres per minute quoted online.
What this means
L9 means the control has measured low flow in a primary water circuit. The manual lists it three times for three circuits: heat source side sensed by the flow sensor, then Zone1 and Zone2, each sensed by a flow switch. The digit shown in Request code 569 under Running information tells you which of the three it is. It reports a measurement, not a failed pump.
Equipment and model context
Ecodan FTC5 cylinder units, EHPT20X-MHCW and EHST20(D)(C)-MHCW
- Ecodan EHPT20X-MHCW packaged cylinder units
- Ecodan EHST20(D)(C)-MHCW split cylinder units
- Packaged outdoor units PUHZ-W50 to PUHZ-HW140 and split outdoor units SUHZ-SW45 to PUMY-P140
Scoped to the FTC5 controller as documented in the EHPT20X-MHCW and EHST20(D)(C)-MHCW cylinder service manual. Later FTC generations and the newer Ecodan ranges carry their own code tables, and a code letter shared between two controllers is not a shared meaning.
What you may notice
- L9 on the main controller with heating off and the system in a fault state.
- L9 appearing shortly after a filling, a drain-down, or work on the heating circuit.
- L9 clearing on a restart and returning later without any other symptom.
Likely causes
- Insufficient system head, so the pump cannot move the flow the outdoor unit needs.
- Reduced flow from air in the circuit, a blocked strainer, a leak, or a valve fault.
- A detached connector or terminal on the sensing path, or a DIP switch set for the wrong circuit.
Diagnostic paths
Request code 569 shows 1
The reading came from the flow sensor on the heat source side, which is the circuit between the outdoor unit and the cylinder.
This is the branch where the recommended water flow rate range for the specific outdoor unit applies. The manual names insufficient system head first and points at whether the system pump meets the requirement, before anything on the sensing side is suspected.
Request code 569 shows 2 or 3
The reading came from a flow switch on Zone1 or on Zone2 rather than from the heat source circuit.
The sensing device is different, so the checks are different. The manual lists the IN3 terminal for Zone1 and IN7 for Zone2, along with the SW3-2 and SW3-3 settings, and a wrong setting produces the code with nothing wrong in the water.
L9 appeared within a minute of the pump starting
The code arrives at the start of a cycle rather than during steady running.
The manual documents an exception for the first minute after water circulation pump1 switches on, so a genuine detection is made outside that window. Record whether the code arrives at start-up or after the system has been running, since that distinction narrows the search.
The circuit was opened recently
The code followed a filling, a drain-down, a radiator change, or a valve replacement.
Air and strainer debris are both on the manual's own cause list, and both are consequences of opening a sealed circuit. Purging and cleaning the strainer are the actions the manual names, and both belong to whoever commissioned the work.
| Request code 569 | Circuit | Sensing device |
|---|---|---|
| Digit 1 | Primary, heat source side | Flow sensor |
| Digit 2 | Primary, Zone1 side | Flow switch |
| Digit 3 | Primary, Zone2 side | Flow switch |
Where the five litres per minute figure comes from
The number circulating on forums is 5 litres per minute, described as the flow below which the Ecodan reports L9. That figure exists in the manual, but it is the minimum flow rate the flow sensor is set to detect, adjustable from the Auxiliary settings menu, with a note telling the reader not to change it because it matches the sensor's specification.
The figure that describes what the system needs is a different table entirely. The manual lists a recommended water flow rate range per outdoor unit, and the floor of that range runs from 7.1 litres per minute on a PUHZ-SW40 to 20.1 on a PUHZ-SW120. A system delivering 12 litres per minute is inside the range for a PUHZ-SW40 and well below it for a PUHZ-SW120.
So a reading held up against 5 litres per minute answers the wrong question. The pairing of the flow figure and the outdoor unit model on the plate is what makes the reading mean something.
What the code establishes and what it leaves open
L9 establishes that a sensing device reported low flow for ten consecutive seconds outside the start-up exception. It does not establish that flow was low, because the manual's own cause list ends with a flow sensor or flow switch fault, a detached connector, an incorrect DIP switch setting, and an FTC board failure.
Four of the eight causes listed against the heat source side entry sit on the water side and four sit on the electrical and configuration side. Reading the code as proof of a pump problem discards half the list before any measurement has been taken.
The SW2-2, SW3-2, and SW3-3 entries deserve separate mention because they are the ones that produce the code on a system with no fault in it. A switch set for a circuit that was never installed leaves the control watching for a flow that nothing was ever going to produce.
Why the primary circuit runs short in an installed system
Head is the mechanism behind the first cause. A circulation pump produces a pressure difference, and the circuit consumes it through pipe runs, bends, valves, the plate exchanger, and the emitters. If the consumption exceeds what the pump can produce at the required flow, the flow settles lower, and the manual's remedy is to add a pump of the same size or fit one with more capacity.
Air does the same thing by a different route. A pocket of air in a high point reduces the effective cross-section of the circuit and can stop a pump moving water at all, which is why purging appears alongside strainer cleaning in the same cause entry.
Neither is a fault in the heat pump. Both are properties of the water circuit around it, which is why the code lands on the installer or the maintaining engineer rather than on a warranty claim against the outdoor unit.
| Outdoor unit | Range in litres per minute |
|---|---|
| PUHZ-SW40 | 7.1 to 11.8 |
| SUHZ-SW45 | 7.1 to 12.9 |
| PUHZ-W50 | 7.1 to 14.3 |
| PUHZ-SW75 and PUHZ-SHW80 | 10.2 to 22.9 |
| PUHZ-W112, PUHZ-SW100, PUHZ-SHW112 | 14.4 to 27.7 |
| PUHZ-SW120 | 20.1 to 27.7 |
| PUHZ-HW140 and PUHZ-SHW140 | 17.9 to 27.7 |
What to give the technician
Give the engineer the Request code 569 digit, the outdoor unit model from the plate, the system pressure reading, and whether the code arrives at start-up or during running. Those four facts choose between the heat source and zone branches and set the flow figure the reading has to be compared against.
Safe homeowner checks
- Read the fault code and then look up Request code 569 in Running information on the main controller, and write down the digit shown.
- Photograph the outdoor unit model number on the data plate, since the recommended flow range is per model.
- Note the system pressure on the gauge and whether the pressure has been falling, since a leak is on the manufacturer's cause list.
- Record whether the code appears at start-up or during steady running, and whether the circuit has been opened recently.
- Check that no radiator valve or zone valve has been closed off since the system last ran normally.
When to call a technician
- Strainer cleaning, purging a sealed system, and any work that breaks into the water circuit belong to the installer or a qualified heating engineer.
- Electrical testing of the flow sensor, the flow switch, the CN1A connector, and the IN2, IN3, and IN7 terminals is technician work on a live control.
- DIP switch settings on the FTC board are commissioning parameters, and changing one without knowing which circuits exist can hide the fault rather than clear it.
- Replacing or resizing the circulation pump is a design decision about system head, not a parts swap.
Questions people ask about this
What does L9 mean on an Ecodan?
Low flow rate in a primary water circuit, detected for ten consecutive seconds. The service manual lists it three times, once for the heat source side sensed by a flow sensor and once each for Zone1 and Zone2 sensed by flow switches, and Request code 569 shows 1, 2, or 3 to identify which.
Is 5 litres per minute the Ecodan minimum flow rate?
That is the minimum flow the flow sensor is set to detect, and the manual instructs that the setting not be changed. What the system needs is the recommended water flow rate range for the outdoor unit fitted, whose floor runs from 7.1 to 20.1 litres per minute across the models in the table.
Can L9 appear when the pump is working?
Yes. The listed causes include a flow sensor or flow switch fault, a detached connector or terminal, an incorrect SW2-2, SW3-2, or SW3-3 setting, and an FTC board failure. Each produces the code without any reduction in the water actually flowing.
Why did L9 appear right after the system was filled?
Air in the circuit and debris in the strainer are both on the manufacturer's cause list, and both follow from opening a sealed system. The manual pairs opening the purge valve with checking the strainer for blockages in the same diagnostic entry.
Does L9 mean the heat pump is faulty?
Not on its own. The first cause the manual names is insufficient system head, which is a property of the pipework, valves, and pump around the heat pump rather than of the outdoor unit. The remedy it names is adding or resizing the circulation pump.
What is Request code 569?
It is an entry under Running information on the main controller that displays a digit alongside the L9 fault. A 1 points at the heat source side, a 2 at Zone1, and a 3 at Zone2, which is the fastest way to know which of the three circuits reported the low flow.
Evidence recordHow this page was checked
service manual · checked 2026-09-07
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Mitsubishi Electric technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- service manual
- Scope of the definition
- Ecodan FTC5 cylinder units, EHPT20X-MHCW and EHST20(D)(C)-MHCW
- Last checked
- 2026-09-07