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Darkforce
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February 9, 2025
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Ecodan and L9 error?

  • February 9, 2025
  • 16 replies
  • 3764 views

Hi everyone, hope your all well! 
 

Just looking for a bit of advise if I may. 
 

we have recently had an Ecodan ASHP installed, worked great for a few days but then noticed it kept giving L9 error every night from 10–11pm. The only think to happen at them times is that the UFH goes off at 10pm but I’m guessing by the time the actuators close etc it’s probably why it happens at random times.

I have changed the UFH to go off at 11:00pm and now L9 happens 11:30ish. Once reset the ASHP is reset the system works lovely, but what’s weird is if I turn the stats down during the day everything works fine. 
Only seems to happen on a night!! 
 

Our installer said Mitsubishi have said it’s a dodgy 2 port valve, which is maybe but he can’t get back for a little while as he’s away at the moment. But if I can get some help it means I pay and get someone else in to fix it but don’t want to throw money at the problem without knowing.

 

thank you 🙏🏻

Best answer by Peter E

Updated on 09/06/25 by Abby_OVO

 

Mitsubishi have a really helpful error code look-up tool. The following information about error code ‘L9’ has been taken from their search tool:

 

Code Text Description Cause Check Procedure Technical Support Notes
L9 Flow sensor or flow switch detecting low flow rate on primary circuit Water circulation issue, air in the primary circuit, zone valve/pump not energising, flow sensor reading abnormal value Check pump/zone valve operation, check connections/wiring of flow sensor and/or switch, check FTC dip switch settings

 

If you’re encountering a different error code, check out the search tool for more information on that code.

 

I’ve recently started asking ChatGPT for the range of ideas of what this could be. It came back with this answer:

 

This is a copy of a conversation between ChatGPT & Anonymous.

 
You said:
A Mitsubishi Ecodan ASHP is giving an L9 error every night at the same time. It has been suggested that the two port valve is faulty. Id that likely to be the cause?
ChatGPT said:

The L9 error on a Mitsubishi Ecodan Air Source Heat Pump (ASHP) typically indicates a low water flow or flow-related issue. This could be due to several causes, and a faulty two-port valve is one possibility, but let's explore it in more detail.

Possible Causes for L9 Error:

  1. Faulty Two-Port Valve:

    • If the valve is not opening or closing correctly, it could restrict water flow, triggering the L9 error.
    • Since the error occurs at the same time every night, it’s possible the valve is programmed or reacting to a timed event (like a scheduled heating cycle).

  2. Flow Sensor Issues:

    • The flow sensor could be malfunctioning, giving a false reading of low flow.
    • Check for debris or dirt on the sensor.

  3. Pump Issues:

    • The circulation pump might be failing or running intermittently, especially if the error is time-specific.
    • Check if the pump is running when the error occurs.

  4. Air Locks in the System:

    • Air trapped in the system can reduce water flow. Bleeding the radiators and system could resolve this.

  5. Blocked Filters or Strainers:

    • Dirty or clogged filters can restrict flow, especially if debris builds up during the day and triggers the error at night.

  6. System Pressure:

    • Low system pressure could contribute to flow issues. Ensure the pressure is within the recommended range.

  7. External Timers or Controls:

    • If there's an external control system or timer, it could be interacting with the ASHP in a way that restricts flow at night.

Troubleshooting Steps:

  1. Check the Two-Port Valve:

    • Manually operate the valve to see if it moves freely.
    • Listen for any unusual noises or check if the actuator is getting power when it should open.

  2. Inspect Flow Rates:

    • Check the flow sensor readings and see if they drop before the L9 error appears.
    • Monitor the pump to ensure it’s running consistently.

  3. Look for Patterns:

    • Since the error is time-specific, consider if other equipment (like thermostats or timed controls) is triggering the issue.

  4. Consult Error Logs:

    • If the Ecodan has a diagnostic mode, review the error logs to see if there’s more detailed information.

Is the Two-Port Valve Likely the Cause?

Given that the error happens at the same time every night, it could point to the valve being controlled incorrectly or failing under certain conditions. However, it’s equally possible that a timer-related issue, pump failure, or flow sensor problem could be to blame.

It’s worth testing the valve first as it's a common culprit, but keep other flow-related components in mind if the problem persists.

Let me know how it goes or if you need more specific steps!

 

Messages beyond this point are only visible to you

 

 

 
 
 
 
 
 
ChatGPT can make mistakes. Check important info.
 
 
 
 
 

16 replies

Chris_OVO
Community Manager
Chris_OVO
Community Manager
February 11, 2025

Hey ​@Darkforce, 

 

Welcome to the community! I’ll tag a few of our members from other Ecodan threads who might be able to offer some advice. We’re not experts in Ecodan by any means but we’ll see what we can offer 😃

 

​@M.isterW ​@amanda1 ​@razor ​@BPLightlog ​@Peter E - Are any of you familiar with the issues that ​@Darkforce has encountered above?

Renewable energy jokes never get old.
    Peter E
    Super User
    Peter ESuper User
    Super User
    February 11, 2025

    I'm mostly offline this morning but I would suggest looking to see if that part is known to be faulty on the Ecodan by looking for comments on an Ecodan forum. I'll be back later ...

    Reducing my yearly fossil fuel usage with an EV (-900 litres petrol), A2AHP (-8,700 kWh gas) and Timed Immersion heater (-1,500 kWh gas)
      BPLightlog
      Super User
      BPLightlogSuper User
      Super User
      February 11, 2025

      Not sure I can help much … L9 is a flow error from what I understand. 

      Bring me Sunshine ~ E&E {Solar PV, Battery Storage, Hybrid EV, ASHP and Home Assistant automation}
        Peter E
        Super User
        Peter ESuper UserSolved
        Super User
        February 11, 2025

        Updated on 09/06/25 by Abby_OVO

         

        Mitsubishi have a really helpful error code look-up tool. The following information about error code ‘L9’ has been taken from their search tool:

         

        Code Text Description Cause Check Procedure Technical Support Notes
        L9 Flow sensor or flow switch detecting low flow rate on primary circuit Water circulation issue, air in the primary circuit, zone valve/pump not energising, flow sensor reading abnormal value Check pump/zone valve operation, check connections/wiring of flow sensor and/or switch, check FTC dip switch settings

         

        If you’re encountering a different error code, check out the search tool for more information on that code.

         

        I’ve recently started asking ChatGPT for the range of ideas of what this could be. It came back with this answer:

         

        This is a copy of a conversation between ChatGPT & Anonymous.

         
        You said:
        A Mitsubishi Ecodan ASHP is giving an L9 error every night at the same time. It has been suggested that the two port valve is faulty. Id that likely to be the cause?
        ChatGPT said:

        The L9 error on a Mitsubishi Ecodan Air Source Heat Pump (ASHP) typically indicates a low water flow or flow-related issue. This could be due to several causes, and a faulty two-port valve is one possibility, but let's explore it in more detail.

        Possible Causes for L9 Error:

        1. Faulty Two-Port Valve:

          • If the valve is not opening or closing correctly, it could restrict water flow, triggering the L9 error.
          • Since the error occurs at the same time every night, it’s possible the valve is programmed or reacting to a timed event (like a scheduled heating cycle).

        2. Flow Sensor Issues:

          • The flow sensor could be malfunctioning, giving a false reading of low flow.
          • Check for debris or dirt on the sensor.

        3. Pump Issues:

          • The circulation pump might be failing or running intermittently, especially if the error is time-specific.
          • Check if the pump is running when the error occurs.

        4. Air Locks in the System:

          • Air trapped in the system can reduce water flow. Bleeding the radiators and system could resolve this.

        5. Blocked Filters or Strainers:

          • Dirty or clogged filters can restrict flow, especially if debris builds up during the day and triggers the error at night.

        6. System Pressure:

          • Low system pressure could contribute to flow issues. Ensure the pressure is within the recommended range.

        7. External Timers or Controls:

          • If there's an external control system or timer, it could be interacting with the ASHP in a way that restricts flow at night.

        Troubleshooting Steps:

        1. Check the Two-Port Valve:

          • Manually operate the valve to see if it moves freely.
          • Listen for any unusual noises or check if the actuator is getting power when it should open.

        2. Inspect Flow Rates:

          • Check the flow sensor readings and see if they drop before the L9 error appears.
          • Monitor the pump to ensure it’s running consistently.

        3. Look for Patterns:

          • Since the error is time-specific, consider if other equipment (like thermostats or timed controls) is triggering the issue.

        4. Consult Error Logs:

          • If the Ecodan has a diagnostic mode, review the error logs to see if there’s more detailed information.

        Is the Two-Port Valve Likely the Cause?

        Given that the error happens at the same time every night, it could point to the valve being controlled incorrectly or failing under certain conditions. However, it’s equally possible that a timer-related issue, pump failure, or flow sensor problem could be to blame.

        It’s worth testing the valve first as it's a common culprit, but keep other flow-related components in mind if the problem persists.

        Let me know how it goes or if you need more specific steps!

         

        Messages beyond this point are only visible to you

         

         

         
         
         
         
         
         
        ChatGPT can make mistakes. Check important info.
         
         
         
         
         
        Reducing my yearly fossil fuel usage with an EV (-900 litres petrol), A2AHP (-8,700 kWh gas) and Timed Immersion heater (-1,500 kWh gas)
          Peter E
          Super User
          Peter ESuper User
          Super User
          February 11, 2025

          I’ve taken to exploring how useful ChatGPT answers are and in general the seem to be lesss precise/detailed than you might want but it does seem to provide a variety of possible causes well beyond I would have thought of myself. I can only suggest you read through and try the practical steps that you can take yourself as it may be able to narrow the fault a bit more.

           

          If it’s a normal plumbing job then you could call a plumber instead of a heat pump engineer. I do a similar thing for my EV. I get my local garage to fix the mechanical issues which don’t involve any of the EV parts.

           

          Peter

           

          Reducing my yearly fossil fuel usage with an EV (-900 litres petrol), A2AHP (-8,700 kWh gas) and Timed Immersion heater (-1,500 kWh gas)
            D
            Rank 1
            DarkforceAuthor
            Rank 1
            February 11, 2025

            Hi all,

            Really appreciate all the help, and happy to say it’s all sorted. 
            Turns out the auto bypass valve wasn’t passing, so a new one has been installed and should be good 🤞🏻

            Error was only happening during the freeze stat cycle so helped narrow the fault down.

             

            Thanks again all 😀

              Peter E
              Super User
              Peter ESuper User
              Super User
              February 11, 2025

              Thanks for the feedback on how the fault was fixed. This is always greatly appreciated.

               

              Experienced Engineer 1: ChatGPT 0

               

              Peter

              Reducing my yearly fossil fuel usage with an EV (-900 litres petrol), A2AHP (-8,700 kWh gas) and Timed Immersion heater (-1,500 kWh gas)
                Chris_OVO
                Community Manager
                Chris_OVO
                Community Manager
                February 12, 2025

                Amazing work ​@Darkforce thank you so much for coming back and letting us know the outcome. This’ll be really helpful as we have a good sized Ecodan community that come seeking advice 😍

                 

                Thank you again to ​@Peter E and ​@BPLightlog for also stopping by! I loved the creative thinking asking AI for it’s take on it Peter! 

                Renewable energy jokes never get old.
                  Peter E
                  Super User
                  Peter ESuper User
                  Super User
                  February 12, 2025

                  To be honest you are not going to beat an experienced engineer but using the output generated by AI may trigger a thought as to what the problem is and may result in not having to call out an engineer in the first place. The alternative is sifting pages of mostly irrelevant search results. AI seems to cut that out and it also asks you if you want to refine the results by supplying information to specific questions. A simple Google search doesn't do that. What you mostly get is ranting between plumbers.

                  Reducing my yearly fossil fuel usage with an EV (-900 litres petrol), A2AHP (-8,700 kWh gas) and Timed Immersion heater (-1,500 kWh gas)
                  juliamc
                  Rank 20
                  juliamc
                  Rank 20
                  February 12, 2025

                  I wonder if the problem with a bypass valve might now appear in the AI search results ?

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