no heat, natural gas forced air
I had no heat from my natural gas forced air furnace, the blower was running, but no heat in any vent. First I changed the filter, which helped. However, a few days later, it happened again. I turned off the unit at the thermostat and back to heat with no change. I then went to the fuse box. The furnace breaker was not tripped, but I turned it off and then back on. The heat started working again. This has happened 3 times in the past week. The unit is about 17 years old. Any thoughts?