We were sitting on watching TV tonight talking about how cold it is -24 when I said why is it not getting any warmer in here? We checked the temp and the inside temp was down to 65 but the set temp is set at 70. We went down to look at the furnace changed the air filter and replaced batteries on digital thermostat now it will not reach set temp and if it shuts off the burners will not turn on unless you blow on them.

Are you on propane or NG? Sometimes this is caused by low gas pressure and at -24 propane might be slow to vaporize.