no heat, natural gas forced air

rossk

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?

biggles

do you have AC with the furnace and was the filter packed with dust...if it was check the squirrel cage round fins make sure they are not covered with dust(run your index finger down a couple).if you have and AC coil above the burner and the filter was packed with dust the next place is the fan section then onto the coil fins..if you can see light thru the filter it shouldn't be that.17 years old running there isn't much electronics within the furnace so that reset has to be an over temperature trip(heat comes up but the fan is not pulling the heat off the exchanger) thats giving you no air or random runs...put the fan in the ON position at the stat,and set the heating as normal see if you trip then!by putting the FAN in the ON position it will run constantly heat or no heat.when it is in AUTO the fan cycles thru the furnace as the temperature rises then cycles OFF as the heat cools down.