Since July I've been getting periodic L-9 "Low flow rate" system error on my FTC6 (for MITSUBISHI Ecodan PUHZ-W85VAA)   I've checked all filters etc and everything is clean and appears to be free running. The circulation pump is set to maximum flow rate (factory default, as it always was). I'm currently using it in cooling mode only (disabled DHW, doing that with immersion) and still happening. (When I had DHW enabled it happened more often in the DHW phase, but even happens without at