Furnace Pilot Light Is On But No Heat Coming [Fixed]

If your furnace’s pilot light is on but no heat is coming into your home, it can be frustrating and uncomfortable, especially during that cold night. There could be a few reasons for this issue, and this troubleshooting guide will help you identify and possibly fix the problem. Always prioritize safety when working with gas appliances.

A dirty flame sensor is the most common reason your furnace pilot is on, but no heat is coming into your home. To fix this problem, locate the flame sensor in the furnace. It is typically situated near the burners. Unscrew the flame sensor and clean it with a currency bill.

Besides a dirty or bad flame sensor, here are some of the reasons you have a pilot light lit but your furnace is not kicking on;

Bad flame sensor
Bad thermocouple
Open Limit switch
faulty thermostat
Dirty Air filter
Closed vents
Defective blower motor

So, let’s look at the chart below showing the causes for this problem and how to fix each issue before we dive into detailed troubleshooting steps.

Reasons a furnace a Pilot light is on but no heat coming

Cause	Fix
Thermostat issue	Ensure thermostat is correctly set
Bad flame sensor	Clean or replace flame sensor
Bad thermocouple	Clean thermocouple
Open Limit switch
Dirty Air filter	Clean filters
Closed vents	Ensure vents are open and not blocked
Defective blower motor	Check if blower motor is running

Thermostat Issue

Before you proceed to other troubleshooting steps, ensure that your thermostat is correctly set to the “heat” mode, and the temperature is set above the current room temperature.

Sometimes, a thermostat can accidentally be set to “cooling” instead of “heating,” which may cause the furnace not to heat despite the pilot light being on.

Double-check your thermostat settings. If everything appears to be in order, you can then proceed to troubleshoot other potential issues.

Dirty or bad flame sensor

One of the most common reasons for a furnace pilot light being on but the furnace not kicking on is a dirty or malfunctioning flame sensor.

A flame sensor is among the several safety components in a furnace. It appears as a straight rod, sometimes L-shaped, positioned at the rear of the burners. The primary function of the flame sensor is to prevent gas leaks.

Its role involves sending signals to the control board to shut off the gas valve if it fails to detect flames on the burners for approximately 30 seconds after the furnace is turned on.

To remedy the issue, a dirty flame sensor can be easily fixed. You simply need to clean it and reattach it.

This task may require a screwdriver and a Scotch-Brite pad to remove any buildup on the sensor rod. If cleaning the flame sensor does not resolve the problem, you might need to purchase a new flame sensor.

Bad thermocouple

A thermocouple serves as another critical safety device within a furnace. Its function is to detect heat emanating from the pilot light.

If the thermocouple fails to detect this heat, it will trigger the shutdown of the gas valve, ultimately preventing the burners from igniting and, consequently, no heat production.

A malfunctioning thermocouple can occur when it fails to sense the pilot’s heat. This issue can lead to the gas valve shutting off. Several factors can contribute to a bad thermocouple, including:

Dirty buildup on the tube, such as discoloration, cracks, or pinholes.

Wear and tear on the wirings, including missing insulation or exposed wires.

To rectify the problem, attempt to clean the thermocouple to eliminate any dust or buildup.

Additionally, ensure that it is positioned correctly so that it can make contact with and sense the pilot light.

Open Limit switch

The limit switch monitors the temperature of the air round the burners. If the temperature goes beyond the set limit, the limit switch will open and shut off the burners.

This is another safety precaution of the furnace. In other words, when there is overheating in the furnace, the limit switch will open.

Overheating can be caused by things like clogged air filters, or defective blower motors. This is what I will be talking about in the next section.

Sometimes the limit switch may malfunction and remain stuck open. If you believe the high limit switch is bad your may test the open limit switch for continuity and replace it if it doesn’t not have continuity consider replacing it.

Dirty Air filter

If you haven’t felt heat from your furnace and the pilot light is on this could be due to dirty filters.

You might be wondering what the connection is between heating and clogged filters.

But here’s the thing: when you have clogged filters, airflow will be restricted, leading to overheating in the furnace. Overheating also triggers the limit switch to open, which means the burners won’t ignite.

To resolve this issue, you need to inspect your air filters and replace them if necessary.

Closed vents

Closed vents can impede a furnace from effectively heating your home. When supply vents (the vents that release warm air into your rooms) are closed, it restricts the airflow in your heating system.

This restriction can result in several issues, including the restriction of airflow itself.

The constrained airflow can lead to the furnace overheating and trigger the high limit switch to open. When the high limit switch is open, the furnace burners won’t ignite.

To fix the problem ensure that vents and registers are open around your home so that there is proper air flow within the furnace system to avoid overheating in the furnace.

Defective blower motor

A furnace blower motor’s job is to circulate the heat air around your home so that your home is heated.

However when you have a bad blower motor, you may have no heating coming into your home and your furnace could overheat due to the ‘unmoved heated air building up.

Try Calling for heat on your thermostat and check if the blower motor is running. If it’s not you might have to replace the blower motor capacitor or replace the entire blower motor assembly.

Final thoughts

In conclusion, this covers all you need to know about troubleshooting a furnace with a lit pilot light but no heat production. As mentioned earlier, if you do not feel confident in tackling this yourself, please consider reaching out to a local HVAC professional for assistance.

Otherwise, I hope you found this guide helpful. Thank you for reading.

More resources:

https://www.pickhvac.com/furnace/troubleshoot/not-igniting/

https://www.ars.com/blog/furnace-not-igniting