L9 error with Mitsubishi ecodan heat pump

[Michel463]

Hi everyone,

 

Two years ago, I purchased a 14kW Ecodan air-to-water heat pump with R32 refrigerant.

Recently, I decided to install a Wi-Fi remote to monitor the temperature in my living room and control the heating more efficiently. However, after enabling the remote, I encountered an issue where the system displays an L9 error after a few hours, and the heat pump shuts down.

 

Based on my research, this error seems to indicate a flow issue. I have already taken the following steps to resolve it:

1. Cleaned the water filter: I ensured there was no debris or blockages in the system.
2. Checked the water pressure: It is approximately 1.6 bars when the system is off, which seems to be within the acceptable range.
3. Increased the pump speed: I set the pump speed to level 5 to rule out insufficient flow as the cause.

Unfortunately, none of these actions resolved the issue.

During my observations, I noticed something unusual: the circulatory pump does not start even when the room temperature is below the set temperature. The pump only starts if I manually trigger it through the heat pump settings. Once it starts, it operates normally, which suggests the pump itself is not faulty.

Additionally, I activated the feature to display the ambient temperature reading, and the values seem accurate. This makes it even more puzzling why the circulatory pump fails to start automatically.

 

At this point, I am left without heating and am unsure how to proceed.

Does anyone have any insights into the cause of the L9 error or potential solutions to this issue?

 

Thank you in advance for your help!

[Dillsue]

I know nothing about your set up but logic says that if the problem occurred after enabling the remote control, it's something to do with the way the remote is controlling things. If you revert back to exactly how things were before adding the remote then see if the fault clears. If it does, you've pretty much ruled out any problems with plumbing/pumps/filter etc and can focus on things the remote is doing wrong

[nod]

We’ve had this twice 

The installer is out tomorrow or Weds 

He seams to think it’s air between the pump and the buffer tank 

He said in any case it’s a flow problem 

man’s will be easy to find 

I’ll keep you posted 

[sharpener]

3 minutes ago, nod said:

He seams to think it’s air between the pump and the buffer tank 

 

Why wouldn't the pump just push the air into the buffer, which presumably has an AAV at the top?

[Michel463]

Hi,
I don’t think it’s an air issue because I manually forced the pump to run all night to clear out any air bubbles, but I’m still getting the same error.

Also, I’ve noticed something strange: the system doesn’t start the pump automatically, which eventually causes the fluid in the machine to overheat, leading to the L9 error.

Do you have any ideas why this might be happening?

[nod]

Just to follow on from earlier 

The installer has been out checked everything Tweaked a few bits 

He said it can only be the flow switch 

He will order one from Mitsubishi in the morning 

[joth]

This comes up every few months. Probably more now it's winter and working harder

 

Here's my experience 

Despite all the advice to the contrary, after trying everything else I just disabled the flow sensor dip switch and it's seemingly been working fine ever since...

I'm trying to get hold of a replacement sensor to swap in and confirm if it's the fault. Unfortunately they're expensive and hard to get hold of 🫤