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ASHP Ecodan L9 error - No Heating but Hot Water

 
Air Source Heat Pumps (ASHPs)
Last Post by Phoenix15 5 hours ago
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 Phoenix15
(@phoenix15)
Active Member Member
Joined: 5 months ago
Posts: 3
Topic starter 21/11/2024 2:31 pm  

My Mitsubishi Ecodan seems be be failing. I am getting a persistent L9 error which seems to indicate flow rate issues. My hot water still works fine and when this is running alone, no errors appear. The heating (rads upstairs, UFH downstairs via Heatmiser) does not work and the error appears when it comes on. I have checked the filter and a little debris appears but nothing major. The hot water pipes are all hot but none of the heating pipes are getting warm. I bled the rads upstairs but there was no air in them. Any idea what the issue could be before I call in a plumber? Has anyone suffered the same before?


   
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 dnagre
(@dnagre)
New Member Member
Joined: 5 months ago
Posts: 2
29/11/2024 9:28 am  

I'm having exactly the same issue, so would also be interested if anyone has advice on this matter. I've followed the support videos from mistibishi but no luck. My problem got progressively worse over a few days. My 3 way valve changes over from water  to heating perfectly fine, and there's piping hot water just after, so I know it's not that. When you feel the pipes the hot water doesn't seem to get passed the vertical pipe after the 3 way valve - not sure what's stopping it. 


   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 4 years ago
Posts: 3109
29/11/2024 12:37 pm  

I reached out to Mitsubishi to provide potential insight into your issue. 

L9 errors could arise from several factors, but ultimately, they indicate the system isn’t happy with the flow rate or can’t detect the flow. This situation typically requires a heating engineer to inspect the system.

The fact that your hot water mode works fine suggests that the heat pump, primary circulating pump, and flow sensor are functioning correctly. Assuming there isn’t an airlock, the issue likely lies with the zone valve or pump(s) on the heating side not operating as expected.

Recommendations:

  • System Pressure: Check that the system is pressurised correctly.
  • Air in the System: Ensure there’s no trapped air in the syste
  • Settings: Verify that the DIP switches and the Main RC settings are configured properly.
  • Valves and Pumps: Use a multimeter to confirm that the valves and pumps are being energised by the FTC controller.
  • Multiple Circuits: If there are two heating circuits (e.g., radiators and underfloor heating), try isolating one. Start with the radiator circuit open and the underfloor circuit closed, and then reverse the configuration.
  • Underfloor Heating Pump: Many underfloor heating manifolds include a dedicated pump, which could be causing the issue.

L9 indicates a flow rate issue when the system detects less than 5 l/min. The Mitsubishi ME Engineer App includes specific checks for this scenario.

The Homeowner Help-Line may request the make and model to provide tailored advice. They can also review fault logs via MelCloud to pinpoint the exact issues. Please call them.

If the hot water works properly, it’s likely the issue is on the secondary side (e.g., radiators or underfloor heating circuits). For example, if only one underfloor heating loop is calling for heat and the flow rate is below 2 l/min, the system will trigger an L9 fault.

To confirm flow rates, access the controller’s service menu, navigate to Running Information, and enter the code 540. The flow rate (in l/min) will display above the code.

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 dnagre
(@dnagre)
New Member Member
Joined: 5 months ago
Posts: 2
30/11/2024 9:10 pm  

Thanks for this Mars. I've actually found out the issue, so this could potentially fix your problem Phonix. 

It was the 'head' of the 3 port valve. It was seizing up inside the body - the heating side anyway.

A little wd40 and it seems to be working, but will have to order new one ASAP before it seizes again. 


   
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 Phoenix15
(@phoenix15)
Active Member Member
Joined: 5 months ago
Posts: 3
Topic starter 20/03/2025 3:34 pm  

@dnagre delayed reply! It worked again for a bit but has started up with the L9 error again and I have noticed the valve is making a noise when trying to switch from heating to hot water- not a good noise. May sound like a silly question but how did you add wd40 to it? There's nothing I can see to remove or move to add anything like this. Thanks in advance!


   
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 Phoenix15
(@phoenix15)
Active Member Member
Joined: 5 months ago
Posts: 3
Topic starter 15/04/2025 7:38 pm  

I since checked the magnetic filter again and there was quite a lot of debris that flushed through. I've been trying to find the other Y filter and can only find the attached in my indoor system.. I'm not sure this is a filter though as its vertical? Any thoughts?

20250415 193732

 


   
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