Furnace Clicks but Blower Won’t Start: Troubleshooting and Fixes

The sound Of A Furnace Clicking While The Blower Won’t Start Is A Common Concern For Homeowners Seeking Reliable Heat And Safety. This Article Explains Likely Causes, Step-By-Step Diagnostics, Simple Repairs, Safety Precautions, Estimated Costs, And When To Call A Professional. It Focuses On Practical, Actionable Guidance For U.S. Households.

Symptom	Likely Cause	Quick Fix
Clicking At Furnace Startup	Ignition Or Relay Attempts; Control Board Commands	Check Power, Reset Breaker, Observe Sequence
Blower Does Not Run After Ignition	Blower Motor, Relay, Limit Switch, Capacitor, Or Control Board	Inspect Motor Power, Test Capacitor, Replace Relay
Intermittent Blower Function	Overheating, Failing Motor, Loose Wiring	Clean Vents, Tighten Connections, Monitor Runtime

How A Typical Gas Furnace Startup Sequence Works

Understanding The Normal Startup Sequence Helps Identify Where The Process Stops When The Furnace Clicks But The Blower Won’t Start. A Typical Sequence: Thermostat Calls For Heat, Ignition Control Initiates Spark Or Hot Surface Igniter, Gas Valve Opens, Burner Lights, Flame Sensor Confirms Combustion, Control Board Signals Blower To Start After A Short Delay.

If Clicking Occurs During This Sequence, It May Indicate The Ignition System Is Trying To Light Or The Control Board/Relay Is Attempting To Power The Blower. Identifying The Exact Stage Of Failure Narrows Down The Troubleshooting Path.

Common Causes And How They Produce The Symptom

1. Faulty Blower Motor

The Motor May Be Seized, Have Burned Windings, Or Suffer From Worn Bearings. A Failing Motor Often Draws Excess Current, Trips Safety Devices, Or Fails To Start While The Control Tries To Engage It — Producing Clicking Sounds From Relays Or The Ignition System.

2. Bad Blower Relay Or Contactor

The Relay Or Contactor Is The Electrical Switch That Connects The Motor To Line Voltage. Clicking Is A Classic Sign Of A Relay Coil Engaging Without Closing Properly Or Closing But Losing Contact Under Load. Relays Can Burn, Stick, Or Fail Mechanically.

3. Failed Run Capacitor

Many Blower Motors Need A Run Capacitor To Start Or Run Efficiently. A Weak Or Open Capacitor Can Allow The Motor To Humming/Clicking Behavior While It Fails To Spin Up. Capacitor Failure Is A Common Cause When The Motor Tries But Cannot Start.

4. Limit Switch Or High-Temperature Shutdown

Furnaces Have Limit Switches To Prevent Overheating. If A Limit Switch Is Tripped Or Failing, The Control May Allow Ignition Attempts (Clicking) But Keep The Blower Off Or Shut Down The Blower Circuit Until The Condition Clears.

5. Control Board Or Thermostat Issues

A Faulty Control Board May Send Incorrect Signals, Or A Malfunctioning Thermostat Could Cause Erratic Commands. Clicking From The Board Or Relay While The Blower Does Not Receive Power Suggests Control Electronics Or Communication Problems.

6. Safety Interlocks And Door Switches

Most Furnaces Have Safety Switches On Access Panels Or Filters That Prevent The Blower From Running If Panels Are Open Or Filters Are Missing. Clicking May Occur When The Control Tries To Run But An Open Switch Stops Power Flow.

Initial Safety Checks Before Troubleshooting

Turn Off Power To The Furnace Using The Service Switch Or At The Breaker Before Opening The Access Panel. Gas Furnaces Also Require Caution With Gas Lines — If A Gas Smell Is Present, Evacuate And Call Utility/Emergency Services.

Use A Noncontact Voltage Tester When Checking Wires, And Wear Gloves/Eye Protection. If Uncomfortable With Electrical Work, Skip To The “When To Call A Professional” Section.

Step-By-Step Troubleshooting Guide

1. Verify Simple Power And Thermostat Signals

Confirm The Furnace Has Power: Check The Circuit Breaker And Service Switch. Verify The Thermostat Is Set To Heat And The Setpoint Is Above Room Temperature. Listen For Clicks And Note Their Timing Relative To The Thermostat Call.

2. Inspect Air Filter, Vents, And Return Air

A Clogged Filter Or Blocked Return Can Cause The Furnace To Overheat And Shut The Blower Off Via The Limit Switch. Replace Dirty Filters And Ensure Vents Are Open. This Simple Fix Resolves Many Runtime Problems.

3. Check Access Panels And Door Interlock Switches

Make Sure All Panels Are Fully Seated And The Access Switch Is Engaged. Some Furnaces Will Click But Not Run The Blower If A Door Switch Prevents Operation.

4. Observe The Ignition And Blower Timing

With The Furnace Powered, Watch The Ignition Sequence: Clicking For Spark Or Igniter Warm-Up, Burner Lighting, Flame Sensor Response, Then Blower Kick-In After A Delay. Note If The Burner Lights But The Blower Never Starts — This Narrows Cause Toward Blower Motor, Relay, Or Capacitor.

5. Test For Voltage At The Blower Motor

With Power On And The Furnace Commanding The Blower (Use Caution), Measure For Line Voltage At The Motor Terminals. If Voltage Is Present But The Motor Doesn’t Run, The Motor Or Capacitor Is Likely Faulty. If Voltage Is Absent, The Problem Is Upstream (Relay, Control Board, Limit Switch).

6. Inspect And Test The Run Capacitor

Visually Inspect The Capacitor For Bulging Or Leaks. Use A Multimeter With Capacitance Test Capability To Measure The Value. A Capacitor More Than 10% Off Rated Value Or Showing Very Low Capacitance Should Be Replaced.

7. Listen For Relay Clicking And Inspect Relay Contacts

Open The Control Compartment And Identify The Blower Relay. Observe Clicking When The Blower Is Commanded. If Clicking Occurs But No Motor Operation, Consider Replacing The Relay. Worn Contacts Can Fail Under Load Even If The Coil Clicks.

8. Check Motor Bearings And Ability To Spin

With Power Off, Manually Spin The Blower Wheel To Ensure It Turns Freely. Stiff Or Seized Bearings Indicate Motor Replacement Or Lubrication (If Motor Has Oil Ports). Motor Replacement Is Often Required For Seized Bearings.

9. Inspect The Control Board For Fault Codes

Many Modern Furnaces Provide LED Fault Codes. Compare The Blink Pattern To The Manufacturer’s Chart On The Panel. Fault Codes Point Directly To Issues Like Limit Trips, Pressure Switch Failure, Or Board Faults.

DIY Repair Options And When They Work

• Replace Air Filter And Clear Vents: Fast And Low-Cost Fix For Overheat-Related Blower Shutdowns.
• Replace Run Capacitor: Moderate Skill Task; Turn Off Power, Discharge Capacitor Safely, Replace With Identical Microfarad Rating.
• Replace Blower Relay: Straightforward If The Relay Is Accessible; Ensure Correct Voltage/Rating.
• Tighten Wiring And Clean Contacts: Loose Or Corroded Connections Can Prevent Power Delivery.

When To Call A Professional HVAC Technician

Call A Licensed HVAC Technician If Any Of The Following Apply: The Furnace Emits A Gas Smell, The Motor Shows Burn Signs, A Control Board Or Gas Valve Replacement Is Likely, Electrical Troubleshooting Is Beyond Comfort Level, Or Safety Devices Are Triggering Repeatedly.

Professionals Provide Proper Diagnostics, Have Specialized Tools For Gas Controls And Flame Sensor Testing, And Can Ensure Safe, Code-Compliant Repairs.

Estimated Repair Costs And Parts

Item	Typical DIY Cost	Typical Professional Cost (Parts + Labor)
Air Filter	$5–$40	$10–$60
Run Capacitor	$10–$40	$60–$150
Blower Relay/Contactor	$15–$60	$100–$250
Blower Motor Replacement	Not Recommended DIY	$300–$800+
Control Board	Not Recommended DIY	$200–$800+

Costs Vary By Region, Furnace Make And Model, And Labor Rates. Replacing A Motor Or Control Board Is The Most Expensive Repair And May Prompt Consideration Of Furnace Age Versus Replacement.

Preventive Maintenance To Avoid Future Problems

• Replace Furnace Filters Every 1–3 Months Depending On Usage And Filter Type.
• Schedule Annual Professional Tune-Ups To Inspect Bearings, Belts, Electrical Connections, And Heat Exchanger.
• Keep Vents And Return Grilles Clear Of Furniture And Debris.
• Listen For Unusual Noises; Clicks, Hums, Or Squeals Can Indicate Wear Before Failure.
• Ensure Proper Thermostat Calibration And Batteries To Prevent Erratic Calls.

Special Considerations For Electric Furnaces And Heat Pumps

Electric Furnaces And Heat Pumps Use Different Starting Circuits But Similar Blower Components. Clicking With No Blower On In Electric Systems Often Points To Relays Or Control Boards Rather Than Gas Ignition. The Same Voltage And Capacitor Checks Apply.

Troubleshooting Checklist For Technicians And Advanced DIYers

1. Confirm Thermostat Call And Measure 24V Signal To Relay/Control.
2. Check Fuse(s) On The Control Board For Blown Fuses.
3. Measure Line Voltage At Motor When Commanded To Start.
4. Test Capacitor With Capacitance Meter; Replace If Outside Spec.
5. Verify Relay Coil Voltage And Inspect Relay Contacts Under Load.
6. Scan Control Board For Fault Codes And Review Wiring Diagrams.
7. Consider Motor Amperage Draw; High Amps Indicate Binding Or Internal Damage.

Key Takeaways And Action Plan

If A Furnace Clicks But The Blower Won’t Start: Start With Basic Safety And Power Checks, Replace Dirty Filters, Inspect Door Switches, And Observe The Startup Sequence. Test For Voltage At The Motor, Check The Run Capacitor, And Inspect The Blower Relay. Replace Parts As Needed, But Call A Licensed HVAC Technician For Gas System Repairs, Motor Replacement, Control Board Faults, Or If Any Unsafe Conditions Exist.

Document Observations, Sounds, And Fault Codes To Share With A Technician If Professional Service Is Required. Timely Diagnosis And Maintenance Reduce Repair Costs And Improve System Reliability.

For Further Assistance, Seek A Local NATE-Certified Technician Or Contact The Furnace Manufacturer For Model-Specific Troubleshooting Guides And Parts Information.