I have Bryant Gas furnace installed in 2001 (don't have the exact model number with me). We have had no issues with it until 2 weeks ago. Two weeks ago the house started feeling cold and we realized the furnace was at 66 when normally at 68. Went to check furnace and error code 14 (lock out) was flashing on LED. Troubleshooting the error code it led to the diagnosis that the hot surface ignitor wasn't working.

1. replaced the hot surface ignitor
2. cleaned off the heat sensor

Furnace started right up and worked great for a week, until this weekend.

Furnace starts up in the morning and runs fine for about 3 hours. It goes on and off and heats up the house. Then it stops working and once again locks it self out. If we follow steps and override shut off it will fire up again. Then after a few hours locks itself out.

Any ideas what could be wrong?

Not sure if coincidence or not.
1. Seems to run fine when the front panel door is off
2. Will run fine in morning as it only kicks on for an hour and a half before it is programmed to go off for the day.

Thanks