Heat Pump Blower Runs Continuously: Causes and Fixes

The heat pump blower running continuously can indicate simple thermostat settings or serious electrical issues. This article explains common causes, diagnostics, and practical fixes for homeowners, highlighting when to call a professional. It focuses on troubleshooting steps to restore proper blower operation and improve system efficiency.

Symptom	Possible Cause	Typical Fix
Blower never stops	Thermostat fan set to ON	Set thermostat fan to AUTO
Runs after cycles	Delay fan or circulation mode	Check thermostat settings or fan limit
Runs with no heat/cool	Relay/stuck contactor or control board fault	Inspect relays, replace faulty parts
Runs intermittently	Shorted wiring or sensor issue	Trace wiring, test sensors, replace bad parts

How A Heat Pump Blower System Works

The heat pump blower circulates air through ductwork by moving air over the indoor coil and through vents. The blower motor receives signals from the thermostat and control board to start, stop, or adjust speed.

In typical operation the blower runs during active heating or cooling and stops or cycles to AUTO between calls for temperature correction. Understanding normal operation helps identify when the blower running continuously is abnormal.

Common Reasons The Heat Pump Blower Runs Continuously

Thermostat Fan Setting

The most common and simplest cause is the thermostat fan setting being set to ON rather than AUTO. When set to ON the fan will run continuously regardless of heating or cooling demands.

Thermostat Programming Or Malfunction

Programmable thermostats may have schedules or temporary overrides that keep the blower on. A malfunction or software glitch in a smart thermostat can also send incorrect run signals to the blower.

Fan Relay Or Control Board Stuck Closed

A stuck fan relay or a short in the control board can leave the blower motor powered continuously. This electrical fault bypasses thermostat commands and requires component testing and often replacement.

Blower Motor Or Relay Wiring Short

Shorted wiring between the thermostat, control board, and blower motor can create a continuous circuit. Physical damage, rodent chewing, or degraded insulation can produce this condition.

Blower Relay Or Contactor Welded

Relays and contactors can weld closed due to arcing and wear. A welded relay will keep the blower energized until the relay is replaced.

Continuous Circulation Or Fan Delay Feature

Some systems intentionally run the blower continuously for air circulation or to balance temperature. Additionally, a fan delay feature may run the blower after the compressor shuts off to capture residual heat or coolness.

Faulty Fan Limit Switch Or High-Limit Control

On some systems the fan limit or high-limit controls control blower operation. A failed sensor may provide incorrect signals keeping the blower on as a safety or error response.

Safety And Diagnostic Precautions

Before any diagnostic work, turn off power at the thermostat and the outdoor disconnect or breaker. Working on HVAC electrical systems carries shock and equipment-damage risks.

If the homeowner is not comfortable with electrical testing use a licensed HVAC technician. Incorrect troubleshooting may void warranties or create hazards.

Step-By-Step Troubleshooting Guide

Check Thermostat Fan Setting

Confirm the thermostat fan is set to AUTO. If using a smart or programmable thermostat, verify there are no active overrides or schedule settings that force continuous fan operation.

Reset Thermostat And Observe

Perform a thermostat restart by removing batteries, powering off for one minute, or using the reset option. After power restoration, observe blower behavior for a full cycle to see if the issue persists.

Inspect Thermostat Wiring

Remove the thermostat cover and inspect wiring for loose or bridged wires. The G wire controls the fan; ensure it is connected properly and not shorted to R or C. Take a picture before disconnecting any wires.

Test Fan Relay And Control Signals

With the system powered on, measure voltage at the control board G terminal when the blower runs. If G is energized with the thermostat on AUTO and not requesting fan, the thermostat or wiring is likely at fault. If G is not energized but the blower runs, the relay or control board is likely stuck.

Inspect The Blower Relay And Contactor

Locate the indoor air handler control board and visually inspect relays for burned contacts or welded terminals. Test continuity across relay contacts when de-energized. Replace relays with exact or equivalent parts when needed.

Check For Shorted Wires Or Sticking Connectors

Trace G wire continuity back to the thermostat. Use a multimeter to check for shorts to R, C, or ground. Repair or replace damaged cable runs and secure loose connectors.

Evaluate The Blower Motor And Capacitor

A failing motor or start/run capacitor can behave erratically, though continuous running is less common as a result. Inspect motor wiring and test capacitor values. Replace a weak or bulging capacitor.

Review Fan Delay And Continuous Circulation Settings

Consult the air handler and thermostat manuals for fan delay, circulation, or IAQ settings. Disable continuous circulation features temporarily to test if those settings are the cause.

When To Call A Professional HVAC Technician

Call a professional if diagnostics point to a stuck relay, control board failure, complex wiring issues, or motor replacement. A licensed technician handles advanced electrical testing, motor removal, and safe control board replacement.

Professional inspection is also recommended if the blower runs continuously after replacing the thermostat or if recurring issues persist despite basic repairs.

Preventive Maintenance To Avoid Continuous Blower Issues

Schedule annual HVAC service to inspect relays, controls, and blower motors. Regular maintenance reduces the likelihood of welded contacts and control failures.

Replace air filters on schedule. Restricted airflow can cause control logic to behave unpredictably, though it more commonly results in short cycling or overheating rather than continuous blower operation.

Cost Estimates For Common Fixes

Issue	Typical DIY Cost	Typical Professional Cost
Thermostat reprogramming	$0–$50	$50–$150
Thermostat replacement	$50–$300	$150–$400 installed
Relay replacement	$10–$50	$75–$250 installed
Control board replacement	Not recommended DIY	$200–$800
Blower motor replacement	Not recommended DIY	$400–$1,200

Tips To Reduce Energy Waste If Blower Runs Continuously

• Set thermostat fan to AUTO when continuous circulation is not required.
• Use programmable or smart thermostats to schedule fan operation efficiently.
• Install a variable-speed blower or ECM motor to reduce energy use during continuous operation.
• Use zoning systems to minimize unnecessary fan running in unoccupied areas.

Common Misconceptions About Continuous Blower Operation

Continuous blower operation is not always harmful; some homeowners intentionally run fans for improved air mixing or filtration. However, continuous running increases energy use and may accelerate wear on parts.

Another misconception is that a new thermostat will always fix the problem. While a faulty thermostat is common, underlying electrical faults at the control board or relay may persist after replacement.

Useful Diagnostic Tools And Replacement Part Tips

A multimeter for voltage and continuity, a clamp ammeter to measure motor current, and a basic screwdriver set are essential for homeowners who perform basic diagnostics.

When replacing parts choose OEM or certified aftermarket components. Note motor part numbers and relay coil voltages to match replacements accurately and avoid compatibility issues.

Frequently Asked Questions

Can a dirty filter cause the blower to run continuously?

Dirty filters typically reduce airflow and can cause overheating or reduced efficiency; they rarely cause continuous blower running directly, but they contribute to system strain and may indirectly affect control behavior.

Is continuous blower operation dangerous?

Continuous operation is generally not dangerous but increases wear, energy use, and may expose electrical faults that could become hazards if left unrepaired. Prompt diagnosis is advisable.

Will a fan relay replacement fix the issue?

Replacing a stuck or welded fan relay often resolves continuous blower issues when the relay is the root cause. Verify the problem with electrical tests before replacement.

Resources And Further Reading

Refer to the air handler and thermostat manufacturer manuals for wiring diagrams and settings. Government energy sites and reputable HVAC associations provide guidance on efficient blower operation and motor choices.

For persistent issues consult an NATE-certified HVAC technician for accurate diagnosis and safe repairs.

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