Gas Valve
Gas valve operation and gas pressure.
Furnace Blowing Cold Air: A Diagnostic Order That Finds It Fast
Why a gas furnace blows cold or lukewarm air, in the order to check it: thermostat fan setting, lockouts, flame proving, limits, gas supply, and duct leaks.
How to Check Furnace Gas Pressure: Inlet and Manifold with a Manometer
Step by step for measuring furnace inlet and manifold gas pressure with a manometer, typical ranges for natural gas and propane, how to adjust, and how to clock the meter.
How to Test a Furnace Hot Surface Igniter (and Why They Keep Failing)
How to test a hot surface igniter by watching the sequence, checking voltage and measuring resistance, the difference between silicon carbide and silicon nitride igniters, and what shortens their life.
Millivolt Wall Heaters and Floor Furnaces: Thermopile and Gas Valve Troubleshooting
How millivolt (powerpile) systems on wall heaters, floor furnaces and fireplaces work, how to test the thermopile, and how to find the voltage drop that keeps the main burner from lighting.
Standing Pilot Won't Stay Lit: Thermocouple Testing on Older Furnaces and Boilers
How a standing pilot and thermocouple work on older furnaces, boilers and water heaters, how to test the thermocouple with open-circuit and closed-circuit millivolt readings, and what else makes a pilot go out.
Furnace Ignition Lockout: Failed Ignition Troubleshooting Step by Step
Diagnose a furnace that tries to light and locks out by following the ignition sequence: inducer, pressure switch, igniter, gas valve, flame sense.