I have a EVCON model 6236-530 installed in 1991. During the recent cold spell it quit putting out heat and actually produced ice chunks inside the panel. Now I have no heat. Any suggestions what to check before spending a lot of money on a service call? O know nothing about furnaces so please use plain talk. Thank you.

Turn off the power and then turn power back on. Make sure thermostat is calling for heat. This will recycle the unit. If this fails then it is time to call for On Site service.