The furnace display or thermostat message “Call For Heat” indicates the heating system has detected a request to start heating but is not running due to an identified condition or safety lockout. This article explains what the message means, common causes, diagnostic steps, and safe troubleshooting for homeowners and technicians.
| Issue | Likely Cause | Quick Action |
|---|---|---|
| Thermostat Request | Normal operation | Verify thermostat settings |
| No Ignition | Ignition failure or gas supply | Check gas and power; reset if safe |
| Limit/Safety Lockout | Overheat or blocked vent | Inspect filters, vents; call pro |
| Flame Failure | Pilot/igniter or gas valve issue | Schedule service |
| Control Board Error | Fault code displayed | Note code and reference manual |
Content Navigation
- What “Call For Heat” Means
- How The Heating Sequence Normally Works
- Common Causes For “Call For Heat”
- How To Safely Troubleshoot “Call For Heat”
- When To Call A Professional
- Examples Of Technician Diagnostics And Repairs
- Preventive Maintenance To Avoid “Call For Heat” Messages
- Safety Warnings And Gas Leak Signs
- Understanding Status Messages Versus Error Codes
- Cost Considerations For Repairs
- Frequently Asked Questions
- Key Takeaways
What “Call For Heat” Means
When the thermostat is set above room temperature, it sends a signal to the furnace control board indicating a heat demand. “Call For Heat” is the control board’s status message that a demand exists but the furnace hasn’t completed or can’t complete the ignition and combustion sequence. The message can be benign during the normal start-up sequence or it can be an alert that the system is waiting on a safety condition or troubleshooting step.
How The Heating Sequence Normally Works
Understanding the normal sequence helps interpret “Call For Heat.” Typical steps: thermostat sends a call, inducer fan (if present) starts, pressure switch confirms proper venting, ignition system engages (hot surface igniter or spark), gas valve opens, flame is established, flame sensor confirms combustion, and the burner remains active until the thermostat is satisfied.
Common Causes For “Call For Heat”
Several conditions can cause the furnace to remain at a “Call For Heat” status. Common causes include thermostat wiring or settings, failure of the ignition components, gas supply issues, safety lockouts from high limit or pressure switches, dirty flame sensors, control board faults, or blocked vents and filters.
Thermostat Issues
If the thermostat wiring, batteries, or configuration is incorrect, it may send intermittent or no proper signal. Verify thermostat mode, setpoint, and wiring. A shorted or loose wire on the R, W, or common terminal can prevent ignition despite showing a call.
Ignition Failure
Ignition problems include a worn hot surface igniter, malfunctioning intermittent pilot, or defective spark module. The furnace will show a call but fail to light. These parts degrade with age and require replacement by a qualified technician.
Gas Supply And Valve Problems
If the gas supply is interrupted or the gas valve fails to open, the burner cannot light. Causes include a closed shutoff valve, gas service outage, low gas pressure, or a faulty gas valve that will need professional testing and repair.
Flame Sensor Dirty Or Faulty
A flame sensor that is dirty or failing will not detect flame reliably and may cause the control board to shut down the burner after each attempt. Cleaning the flame sensor can often restore operation; replacement may be required if heavily corroded.
Pressure Switch Or Venting Problems
Negative pressure safety switches and sealed combustion venting systems must indicate proper flow before ignition. Obstructions, blockages, or a failing inducer motor can prevent the pressure switch from closing and leave the furnace at “Call For Heat.”
Limit Switch Or Overheat Lockout
High limit switches protect against overheating. If the furnace overheated previously due to airflow restriction or blower failure, the limit may keep the furnace off until it resets or a technician clears the underlying cause.
Control Board Or Error Codes
The control board monitors sequences and will display or flash error codes when faults occur. A persistent “Call For Heat” with an accompanying error code often points to a specific component failure. Recording the code and consulting the manual helps pinpoint the issue.
How To Safely Troubleshoot “Call For Heat”
Safety is paramount. Homeowners should perform basic checks and avoid working on gas or electrical components beyond their comfort level. If uncertain, call a licensed HVAC technician. Recommended initial checks are simple and non-invasive.
- Confirm Thermostat Settings: Ensure the thermostat is set to heat and temperature is set above room temperature. Replace batteries if applicable.
- Check Power: Verify furnace has power—check circuit breakers and the power switch near the furnace. Some units have a switch that looks like a light switch; ensure it is on.
- Inspect Air Filter: A clogged filter restricts airflow and can trigger limit switches. Replace filters if dirty.
- Examine Vents And Intake: Make sure exhaust and fresh-air intakes are clear of debris, snow, or nests.
- Reset The Furnace: If the manual allows, turn off power for 60 seconds and restore power to reset control board. Do not repeatedly reset without diagnosing the cause.
- Check For Error Codes: Look for flashing LEDs or codes on the control board or display and note them for a technician.
When To Call A Professional
Call a licensed HVAC professional when ignition components, gas systems, pressure switches, control boards, or complex electrical diagnostics are involved. Also contact a pro if there is any suspicion of a gas leak, unusual odors, persistent lockouts, recurring flame failures, or if the homeowner is uncomfortable performing basic checks.
Examples Of Technician Diagnostics And Repairs
A service technician will typically follow a systematic diagnostic approach: verify thermostat signal, measure voltage at the gas valve and igniter, test pressure switch continuity, inspect venting and inducer operation, clean or replace the flame sensor, and read control board fault codes. Replacement parts may include igniters, flame sensors, pressure switches, or the gas valve.
Preventive Maintenance To Avoid “Call For Heat” Messages
Regular preventive maintenance reduces the incidence of lockouts and extends furnace life. Recommended tasks: annual professional tune-up, filter changes every 1–3 months, keeping vents and intakes clear, ensuring adequate combustion air, and scheduling inspections for aging equipment.
Safety Warnings And Gas Leak Signs
Recognize gas leak signs such as a sulfuric or rotten egg odor, hissing near the gas line, or sudden loss of pilot flame. If a gas leak is suspected, evacuate, avoid creating sparks, do not operate electrical switches, and call the gas company or emergency services immediately.
Understanding Status Messages Versus Error Codes
“Call For Heat” is a status message indicating demand and waiting state. It differs from explicit error codes that identify faults. Combining the status message with LED flashes or numerical codes gives technicians a faster path to diagnosis. Homeowners should note both the message and any blinking patterns.
Cost Considerations For Repairs
Costs vary widely depending on the failed component. Simple fixes like filter replacement or cleaning a flame sensor are low cost. Replacing igniters or flame sensors is moderate, while gas valves, control boards, or inducer motors are more expensive. Always request a written estimate and ensure technicians are licensed and insured.
Frequently Asked Questions
Is “Call For Heat” Dangerous?
By itself, the message is not immediately dangerous; it indicates a request that hasn’t been fulfilled. However, it can signal safety lockouts related to airflow, combustion, or gas supply. If there is any gas odor or visible damage, treat the situation as an emergency.
Can A Homeowner Fix It?
Homeowners can perform basic tasks: check thermostat, replace batteries, inspect filters, ensure vents are clear, and power-cycle the furnace. Anything involving gas, combustion components, or internal electrical parts should be left to professionals.
Why Does The Furnace Try To Start Repeatedly?
Repeated start attempts often mean the control sees ignition attempts that fail flame detection. This behavior protects against unsafe operation and points toward the igniter, gas valve, or flame sensor as likely causes.
Key Takeaways
“Call For Heat” means the thermostat has requested heat but the furnace is either in the normal start-up phase or is waiting due to a fault or safety condition. Simple homeowner checks can resolve many issues, but professional diagnosis is essential for gas, ignition, venting, and control board problems. Regular maintenance prevents many causes of “Call For Heat” lockouts and ensures safe, reliable heating.
For persistent or unclear issues, record any error codes, note the furnace behavior, and contact a licensed HVAC technician or the local gas utility for urgent safety concerns.
Tips for Getting the Best HVAC Prices
- Prioritize Quality Over Cost
The most critical factor in any HVAC project is the quality of the installation. Don’t compromise on contractor expertise just to save money. - Check for Rebates
Always research current rebates and incentives — they can significantly reduce your overall cost. - Compare Multiple Quotes
Request at least three estimates before making your choice. You can click here to get three free quotes from local professionals. These quotes include available rebates and tax credits and automatically exclude unqualified contractors. - Negotiate Smartly
Once you've chosen a contractor, use the proven strategies from our guide — How Homeowners Can Negotiate with HVAC Dealers — to get the best possible final price.