When my gas furnace comes on in the morning, it runs for a few minutes and then shuts off before the set temp is reached. After sitting for a few minutes it will come back on. This cycle seems to continue until the set temp is reached and it seems to be OK the rest of the day. The programmable thermostat turns it down about 4 deg at night. I can force to come back on by cycling the on/off switch at the furnace. The electronic ignighter was replaced last week. Any ideas?