Check burner orifices

What is going on

These furnaces leave the factory with #45 natural gas orifices. You only change them for altitude derate or an LP conversion. What I run into most is an orifice somebody has damaged with the wrong tool, or one that was peened and redrilled. A dent or burr kicks the gas stream sideways, so the flame will not sit right in the burner and nothing you do with the regulator will tidy it up. If the flame looks lazy, lifts, or rolls, look at the orifices before you turn any adjustment screws.

Likely causes

• Dent or burr in orifice causing gas stream deflection
• Orifice peened over and redrilled
• Orifice spud of wrong length substituted
• Orifice partly blocked by debris or rust from the gas line

Check in this order

1. Shut off all gas and electrical power
2. Check the orifice visually for distortion or burrs
3. Check orifice size by the number stamped on it, and compare it to what the furnace needs for fuel type and altitude
4. Remove and install orifices with a box-end wrench to avoid distortion
5. Never peen over and redrill an orifice
6. Replace any orifice with a dent or burr
7. After reassembly check for leaks with an approved method and verify flame pattern and manifold pressure

More furnace guides

• Airflow lower than demanded, furnace runs on low stage when high stage is expected
• Alternate combustion air opening (upflow or horizontal)
• Alternate vent/flue location (upflow or horizontal left)
• Annual inspection checklist
• Auxiliary limit control (location and purpose)
• Auxiliary limit switch open (blower compartment)