A furnace that fails to produce heat typically has a dirty flame sensor shutting down gas flow, a cracked hot surface igniter, low gas pressure, or an open high-limit safety switch.
Diagnostic Guide: Gas Furnace Not Heating
A gas furnace that fails to ignite or delivers cold air out of supply registers leaves your home uncomfortable during winter. Return to our main troubleshooting hub for additional diagnostic assistance.
Step-by-Step Furnace Ignition Sequence Diagnostics
Understanding the normal furnace startup sequence helps isolate where the breakdown occurs:
- Thermostat Calls for Heat: Thermostat sends 24VAC signal to furnace control board terminal R to W.
- Draft Inducer Fan Energizes: Inducer motor starts, creating negative draft pressure that closes the safety pressure switch.
- Hot Surface Igniter Energizes: Silicon igniter element glows bright orange (reaching over 1,800°F).
- Gas Valve Opens: Control board energizes gas valve solenoid, releasing gas across burners.
- Flame Sensor Verifies Ignition: Microamp flame rectifying current passes through flame to control board. If flame is verified, indoor blower energizes after 30 seconds.
Request Fast Local Service Dispatch
Because gas furnace servicing involves high-voltage circuits and combustible natural gas, professional diagnostic testing is essential. Connect with certified heating specialists on our furnace repair service page or inspect repair pricing on our furnace repair cost guide. We serve all areas in Montebello CA.
Frequently Asked Questions
Common questions about heating, cooling, scheduling, and service dispatch in Montebello CA.