Why Will My Furnace Not Stay Lit?

Probably the most common issue when dealing with a furnace that will not stay lit or ignite consistently is a dirty flame sensor. The flame sensor acts as a communication vehicle with the circuit board and tells it when a flame is lit inside the furnace.

Why won’t the flame stay on in my furnace?

Your furnace has a limit switch that keeps it from running if the heat exchanger is too hot. Dirty filters, closed or blocked vents and other blockages in airflow are common causes of an overheated furnace. A bad limit switch. The limit switch may be bad and need to be replaced.

What causes a furnace to light then go out?

Another reason why a furnace ignites then turns off could be related to the flame sensor. This key component senses when the flame is on.Often, dust or dirt covers the sensor. If this happens, the sensor won’t detect the flame, and the result is the furnace shuts down.

What are the symptoms of a bad thermocouple?

If you can’t get the flame to light at all, and you’re sure the gas is on, there’s probably an obstruction in the pilot tube. If the flame lights and goes out when you release the gas control knob after holding it in for the recommended 20 to 30 seconds, that’s the sign of a thermocouple malfunction.

How do I know if my furnace flame sensor is bad?

How do I know if my furnace flame sensor is bad?

1. Switch off the power to your furnace.
2. Close the gas valve.
3. Take out the mounting screw.
4. Carefully pull out the sensor.
5. Inspect the sensor: if the insulation is intact but appears sooty, burnt or slightly corroded, it might only require cleaning.

Why does my furnace keep shutting off after a few seconds?

If your furnace keeps shutting off, it could be due to low airflow. There are several indirect issues that cause low airflow. Dirty Air Filters. If you don’t change your air filters often enough, the filters will become dirty and clogged, which means the heat exchanger retains heat and eventually causes it to overheat.

Why does my furnace only runs for a few minutes?

If your furnace turns off after a few minutes, there is a good chance it is caused by a faulty or dirty flame sensor. This vital component is designed to keep an eye on the gas burner. When it cannot sense that burner, the furnace runs then shuts off and starts again.

How much does it cost to replace a thermocouple on a furnace?

Cost to Replace a Thermocouple on a Furnace
Replacing a thermocouple costs $150 to $250, mostly due to labor time. On older models without an ignitor, it checks to make sure your pilot light is lit. If it’s not, it’ll shut the gas off.

How much does a thermocouple cost?

It costs $150 to $250 to replace a thermocouple. It checks to make sure the pilot light is on. It will shut the gas off if it’s not.

How often should a flame sensor be replaced?

Flame sensor lifespan
If you’ve just replaced the sensor or had a new furnace installed, you can expect the flame sensor to last for about five years. The average lifespan of a furnace is 15 to 30 years, so you can anticipate a flame sensor replacement once or twice over the course of your homeownership.

Where is furnace flame sensor?

burner assembly
WHAT IS A FURNACE FLAME SENSOR? A furnace flame sensor is a very basic part of your furnace. It’s located on the burner assembly and is just a thin metallic rod. It’s usually bent, and it sits just in front of the pilot flame inside the furnace.

How do you fix a short cycle furnace?

The easiest way to fix a furnace that is short cycling is to remove the flame sensor to clean it. Use a sponge or brush to remove the dirt from the sensor. After the part is clean, follow the manufacturer’s instructions to insert the flame sensor into the furnace.

Can a bad thermostat cause a furnace to short cycle?

Your thermostat could also cause the HVAC system to cycle on and off rapidly, a process known as short cycling. Your furnace or central air conditioner spends a good amount of energy simply turning on and off, which is why you want yours to run for at least 15 minutes at a time before shutting off.

Where is the reset button on a furnace?

Locate the reset button on the furnace and press it to reset the furnace. It is usually located inside the blower compartment on the side of the blower motor. Be cautious as the housing may be hot. If the button is popped up, press it down.

Why is my furnace coming on every 5 minutes?

A dirty filter can cause the furnace to overheat. Short cycle time: 2-5 minutes.If the furnace gets too hot, the switch shuts down the furnace. A dirty filter prevents a flow of fresh, cool air into the furnace to be heated and dispersed.

How much does it cost to fix a pilot light?

The thermocouple is an apparatus that senses whether the pilot light is lit and triggers the gas control valve. Repairs typically cost about $150 to have it done professionally, though a new thermocouple itself only costs about $20 on average.

How do you clean a thermocouple?

The best way to clean your thermocouple is to use either a piece of steel wool or the coarse side of a sponge to gently clean off any soot or other remnants. You can use a pencil eraser to clean between the threads of the screw that connects the thermocouple to the control valve of your system.

Is it easy to replace a thermocouple?

Thermocouples are designed to detect a pilot light’s loss of heat and close the gas valve to prevent a gas leak. Replacing a thermocouple is a relatively easy fix that can take less than two hours.

Can you bypass thermocouple on furnace?

Realistically, you have just disabled the thermocouple, but you can also reach in and unclip it from its holding bracket where it meets the pilot light. In most cases it will be held on with a gravity clip, but some are held on with a screw that must be removed with a small screwdriver.

Where is thermocouple on furnace?

Your furnace’s thermocouple is usually located right in the flame of the furnace’s pilot light. Its copper tubing makes it easy to spot. The thermocouple is made up of a tube, a bracket, and wires.

What causes a thermocouple to go bad?

Changes in temperature can cause regular expansion and contraction in metal, which will cause thermocouples to weaken over time. After enough time, metal fatigue can cause a thermocouple to break.If thermocouples start to give out unusual readings, it may be suffering from metal fatigue.