Panasonic Aquarea - H12 error

[Dimitriss]

Hi,

I have a Panasonic Aquarea WH-SDF16C9E8 installed for underfloor heating and it's been running fine for 4 years, but the last 2 months it is throwing H12 error (indoor-outdoor capacity umatched). Strange thing is that the H/T can go on working fine for 5 days and then it could start throwing the error twice a day, and then again after three or four occurrences run again for 5 days.

Any idea what I can do to find the source of this error? Could this be a communication error or that one of the units (indoor/outdoor) is drawing more power for some reason (e.g. water pump is drawing more power because underfloor needs flushing or whatever) triggering the error?

Installer says that's it's probably the outdoor PCB and I should get it replaced.
Thanks!