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Furnace Acting Up? Troubleshooting Guide for Start-Stop Issues

Title: Troubleshooting Guide: Why Your Furnace Keeps Starting and StoppingImagine waking up on a chilly winter morning, only to find your furnace repeatedly starting and then abruptly stopping. Frustrating, right?

Many homeowners have encountered this issue, and the causes can vary. In this comprehensive troubleshooting guide, we will explore the common reasons behind a furnace’s erratic behavior and provide you with practical solutions to help you resolve the issue.

So, let’s dive in!

Common causes of a furnace starting and then stopping

Faulty High Limit Switch

One potential culprit behind your furnace’s on-off cycle could be a faulty high limit switch. The high limit switch serves as a safety device that prevents the furnace from overheating.

When it detects temperatures exceeding the set limit, it shuts off the furnace to prevent damage or fire hazards.

Problems with the Flame Sensor

The flame sensor, often a small rod located near the burners, detects the presence of a flame. If the sensor is dirty or malfunctioning, it fails to confirm that there is a flame present.

As a safety measure, the furnace will shut down to prevent the escape of dangerous gases.

A Bad Flame Rollout Switch

A flame rollout switch monitors the burner flames during ignition. If it senses flames “rolling out” from the burner assembly, indicating a potential hazardous condition, it shuts down the furnace to ensure safety.

A Problem with the Hot Surface Ignitor

The hot surface ignitor (HSI) illuminates the gas burners in modern furnaces. If the HSI is faulty or covered in residue, it fails to ignite the gas, causing the furnace to shut down.

Bad Control Board

The control board serves as the brain of your furnace. If it malfunctions, it can interrupt the normal operation of the furnace, leading to repeated start-stop cycles.

Issues with Your Thermostat

An improperly functioning thermostat can cause a furnace to start and stop erratically. Problems may range from faulty wiring to inaccurate temperature readings, leading to improper furnace control.

Furnace is Overheating

When components like the furnace filter, blower motor, or gas valve are obstructed or malfunctioning, the furnace may overheat. As a safety measure, the furnace might turn on and off repeatedly to cool down.

Restricted Air Flow

Restricted air flow due to a clogged air filter, blocked exhaust or fresh air intake vent, closed room registers, or issues with the ductwork can interfere with the furnace’s ability to function correctly, causing it to shut down intermittently.

An Oversized Furnace

An oversized furnace is not only inefficient but can also lead to short cyclingfrequent on-off cycles. An incorrect load calculation during installation could be the reason behind an oversized furnace.

Solutions and troubleshooting tips

Solutions for a Faulty High Limit Switch

– Troubleshoot the switch for possible malfunctions. – Consult a professional if replacement is necessary.

Solutions for

Problems with the Flame Sensor

– Inspect the flame sensor and clean it if dirty using fine sandpaper or steel wool. – Ensure proper positioning of the flame sensor.

Solutions for a Bad Flame Rollout Switch

– Perform a continuity check to determine if the switch is faulty. – Check for any blocked exhaust vents and clear obstructions.

– Consult a professional to bypass the switch temporarily.

Solutions for a Problem with the Hot Surface Ignitor

– Test the ignitor for proper functionality and replace if needed. – Clean the ignitor gently with a soft cloth or a small brush.

Solutions for a

Bad Control Board

– Schedule an appointment with a professional to diagnose and replace the faulty control board. – Consider getting regular inspections and maintenance to avoid future issues.

Solutions for

Issues with Your Thermostat

– Verify the wiring connections and clean if necessary. – Replace the thermostat if it is outdated or beyond repair.

Solutions for Furnace Overheating

– Change the furnace filter regularly to allow proper air circulation. – Clean the blower motor and ensure its smooth operation.

– Check the gas valve for any malfunctions or blockages. Solutions for

Restricted Air Flow

– Clean the exhaust vent and fresh air intake vent of any debris.

– Ensure room registers are open and unobstructed. – Inspect the ductwork for any leaks or blockages, and seek professional assistance if needed.

Solutions for an Oversized Furnace

– Conduct a load calculation to determine the appropriate furnace size for your home. – Consult a knowledgeable furnace contractor to suggest suitable replacement options.


By understanding the various causes of a furnace starting and stopping, homeowners can troubleshoot these issues effectively and potentially avoid costly repairs or replacements. Remember, if you’re uncomfortable performing any of the troubleshooting steps or aren’t confident in your knowledge, it’s always best to seek assistance from a qualified professional.

Stay warm and enjoy the comfort of a well-functioning furnace!

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