As per the title, I'm having a strange issue with my heat pump that seems to be network related, but doesn't make sense.
First, my setup/equipment: Ubiquiti Unifi USG-3 router with latest FW, AP-AC Lite AP's, USW8 switches, Mitsubishi MSZ-AP71VG(D/KD) heat pump with Wifi Module.
I've had the heat pump for a couple of years, no issues with the wifi module on the LAN, no problems using the Mitsubishi app on my Android phone(s). In the last week the heat pump has not been turning off intermittently (not following the schedule set up via the app), then I lost comms with the heat pump on the app, although my Unifi controller was showing the heat pump as connected via wifi, with good signal strength (heat pump module only runs on 2.4GHz). I physically checked the module in the heat pump and it was displaying a DNS error LED. This is where it gets strange. No other devices on the network have been having issues with DNS that I'm aware of.
I changed the DNS settings on the router (from fixed DNS servers (on Spark Fibre) to auto, which may have picked the same servers, not sure. I rolled back the FW on the AP to an earlier version, just in case - no difference. Rebooted the router, factory reset the wifi module and set it up again (several times). Every time it comes back with the DNS error LED. Everything seemed to be pointing to a faulty wifi module.
I then setup a wifi hotspot on my phone, reset the heat pump module and connected it via the hotspot. DNS error disappeared, heat pump accessible via the phone app. So that seems to point the issue back to my LAN rather than the wifi module. But as mentioned, no other devices on the network, wired or wireless have any issues with DNS - it would be very obviouse quickly if they were.
I'm reaching the limits of my network troubleshooting skills (I've been a Telco engineer for many years, with a crossover into VOiP and WiFi). Am I missing anything obvious??
Any help troubleshooting this would be greatly appreciated.