Thermostat issue and it's cold here!

I have the black Comfort ZC thermostat/furnace controller and it's no longer controlling the front furnace. In heat mode it only shows the front heat pump option but does run the middle furnace ok and in cool mode runs A/Cs without any problem.

Is there a reset button or wire connections I can clean?

Can't tell how to open the front cover either.

Thanks, John