Check for danger before checking the thermostat
If you smell gas, hear a suspected gas leak, see smoke or have a carbon monoxide alarm, leave the building and call emergency services from a safe location. Do not try to restart the furnace or operate switches while investigating a suspected gas leak. Follow PG&E's gas-safety instructions and carbon monoxide guidance; a website form is not the route for reporting a dangerous condition.
Safe checks when there are no warning signs
Check that the thermostat is set to heat and its setting is above the room temperature. Review the programmed schedule, hold setting and any user-replaceable thermostat batteries. A display can be on even when a scheduling or control issue prevents the expected heating call.
Look at the filter if it is in a normally accessible holder and can be checked according to the equipment instructions. Note heavy buildup and whether furniture or belongings block a return grille. Check that ordinary room supply vents are open. These observations help describe an airflow problem; they do not establish that a dirty filter is the only fault.
Observe whether other household power is available and whether the thermostat shows an equipment message. Do not remove the furnace's service cover, open electrical enclosures or reset a breaker repeatedly. If a code is visible through the normal viewing window, write it down without taking anything apart.
Describe what happens when heat is requested
The sequence is useful: nothing happens, a small motor starts but heat does not follow, the blower moves cool air, or the furnace starts and then shuts down. Each points the technician toward different tests. A thermostat screen by itself cannot identify an ignition, gas-supply, blower, control or safety-circuit fault.
For an intermittent problem, note when it occurs, how long the equipment runs and whether it followed a filter change, power interruption or thermostat adjustment. Record what you can observe safely rather than cycling the equipment repeatedly to reproduce a fault.
Know where homeowner checks stop
Leave burner, flame-sensor, igniter, gas-valve, venting, internal wiring and safety-control work to a qualified technician. Do not bypass a door switch or other safety device. If equipment was shut down for a safety reason, keep it off until it has been assessed and cleared for use.
Never heat the home with an oven, outdoor grill or generator indoors. If comfort cannot be maintained while the system is off, make safe arrangements for the household while discussing the available service appointment.
What to have ready for a Concord service request
- Your property address and the best access contact.
- The furnace's approximate age, make and model if already available.
- Whether it does nothing, starts then stops, or blows air without warming the home.
- Any safely observed code, unusual noise or recent work.
- Equipment location and access restrictions, especially for a rental or managed building.
Call to discuss appointment availability; submitting a form does not reserve an arrival time. Before booking, clarify the diagnostic visit scope and charges. Repair authorization and a replacement consultation are separate decisions.
Repair, replacement or a second opinion?
A failed start can have a repairable cause. The decision should be based on the finding, safety, overall equipment condition and the complete options. Age alone does not identify the fault, and a single symptom does not establish that the entire system needs replacement.
Our furnace repair page covers related symptoms. If replacement becomes a reasonable option, compare the installation scope and heat-pump versus gas-furnace running costs before choosing a system.
If the equipment is a heat pump rather than a gas furnace, use our heat-pump no-heat guide for the differences in normal operation and troubleshooting.
Common questions
Why does the thermostat call for heat but the furnace does not start?
Possible causes include thermostat or power problems, an ignition fault, restricted airflow, a blower issue or a safety shutdown. The sequence and any safely visible equipment code help guide diagnosis. The symptom alone does not identify which part should be replaced.
Should I keep resetting a furnace that shuts down?
No. Repeated shutdowns or a breaker that trips again need diagnosis. Do not bypass safety controls or keep forcing the equipment to restart. If there is a gas smell, smoke or a carbon monoxide alarm, leave the building and contact emergency services from a safe location.
Is a no-heat call the same as a replacement estimate?
No. A no-heat diagnostic visit investigates the fault in the current equipment. A replacement estimate defines a proposed installation. Explain both the breakdown and your repair-or-replace question when arranging the visit so the intended scope is clear.