To repair Lennox gas furnace parts, first determine the specific issue, and then replace or clean the failing part. Common problems with Lennox gas furnaces include incorrectly set thermostats, gas supply problems, faulty blower motors and airflow problems.
If a Lennox gas furnace runs just for a few minutes, the furnace might have an improper airflow passing via the burner. Check to be sure that it is getting air from the surrounding area, and check for an obstruction at the air inlet. If the problem persists, examine the flame sensor, and if it is dirty, clean it with a soft abrasive pad.
If the gas furnace is noisy during operation, the blower motor or the blower wheel might be defective. Check to be sure that the blower wheel screws are not loose and that the wheel itself is not damaged. If the noise persists, the blower motor bearings might be worn out, and if necessary, replace the blower motor completely.
If a Lennox gas furnace does not heat, first check to see whether the gas supply valve is on, and if so, check to see if you have run out of gas. Test the thermostat for continuity using an ohmmeter, and replace it if necessary. If the above repair methods do not fix the problem, contact a Lennox professional.