I am getting the fire warning message in my new Monoprice Select Mini V2 which is on the latest firmware. According to the changeling they added thermal runaway protection on this release.
Should I still get this message or is it just the case that octoprint hasn't been updated to reflect this?
Probably the latter. If you can confirm that thermal runaway protection is indeed now enabled (disconnect thermistor or heater, give heatup command, observe), please provide the output of M115 and the output of the initial connection handshake of OctoPrint with your printer so the detection can be adjusted accordingly.
When I get a chance I will do this. I assume I will have to dismantle the printer to disconnect the thermistor.
It's been a while but I recently had my printer replaced and the heater cartridge was not seated correctly. When trying to print or pre-heat the nozzle the printer would halt with a "failed to heat" error after a minute or so. The printer would need to be power cycled to try again.