Will pilot stay lit with a bad thermocouple?

Author: Macey Ortiz I  |  Last update: Thursday, July 24, 2025

The Pilot Lights But Won't Stay Lit 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.

Will the pilot light stay on if the thermocouple is bad?

In summary, a malfunctioning thermocouple will likely cause the pilot light to extinguish because it cannot confirm that the flame is present, leading to a safety shutdown of the gas flow. If you suspect a bad thermocouple, it's advisable to replace it or have a professional inspect the system.

What are the signs of a bad thermocouple?

For a bad thermocouple, you will normally see a high temp displayed, and the controller will immediately go into cool down mode. You are showing heat up mode, and erratic temperature displays.

What's the top reason a pilot light doesn't remain lit?

Conclusion A pilot light that won't stay lit can be due to issues with the gas supply, thermocouple, pilot light assembly, gas control valve, venting, or drafts. By systematically troubleshooting each of these potential problems, you can often resolve the issue yourself.

Why won't my pilot light stay lit with a new thermocouple?

Most of the time the reason a pilot wont stay lit is that the pilot orifice and pilot burner are dirty and need to be cleaned. Clean those first before doing anything else. It's routine maintenance that needs to be done in any case.

TOP 10 Reasons Why the Gas Pilot Light Goes Out & Won't Stay Lit!

How do I know if my thermocouple is not working?

The best way to verify that you need a new thermocouple is to see if your pilot light is lit. If the pilot light can't hold ignition, that means either a problem with the gas supply or, more likely, the need for thermocouple replacement.

Why does my pilot light go out as soon as I release the pilot button?

The flame will go out if you release the knob before it is hot. The thermocouple can become dirty and caked with grit, preventing it from heating up and detecting that the pilot is lit. As a result, the pilot will always go out after you release the reset button.

What does a damaged thermocouple look like?

Failed Thermocouple Symptoms

The first is signs of contamination on the tube, which can include discoloration, cracks, or pinholes. Next, check the wiring for any signs of wear or corrosion like missing insulation or bare wire.

Why does my pilot light stay on but fire goes out?

This can be an indication that your fireplace thermocouple is either bad or worn out. However, if your pilot is lit but the gas fireplace isn't, then there's probably a problem with your thermopile.

Can you clean a thermocouple?

Yes, you can clean a thermocouple, but the task must be done with a light touch. Remove the thermocouple from the process assembly, using a steel wool or emery cloth, lightly clean the tip removing any build up. Cleaning a thermocouple is not a fix for an issue, such as inaccurate readings.

How do I know if I need a new thermocouple?

When you have a thermocouple that is going bad on your water heater, the most obvious sign will be a pilot light that always seems to be going out. If you light the pilot light but then find it extinguished less than a week later, you'll need to closely examine the thermocouple.

Can thermocouples fail intermittently?

Sometimes sensors can break or degrade in harsh environments. You might be suffering from intermittent thermocouple failure or instruments might be showing “Open Circuit”.

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

For those who prefer not to attempt a DIY repair, hiring an HVAC technician is a safer option. The cost for a professional furnace thermocouple replacement usually ranges from $80 to $150, depending on your location and the specific HVAC company. This price includes both the part and labor.

What is the difference between a thermopile and thermocouple?

While both devices are crucial for temperature measurement and control, their specific applications and capabilities vary. Thermocouples are primarily used for direct temperature measurement and safety controls, whereas thermopiles are preferred for applications requiring higher sensitivity and voltage output.

Will a bad thermostat cause the pilot light to go out?

Air in the gas line: Enough air in the gas line will put out the pilot light. This is an issue a professional will need to diagnose and take care of. Problems with the thermostat: The thermostat can also impact the pilot light. It must be fixed or replaced to resolve the issue.

Why does my pilot light keep going out after replacing the thermocouple?

Once you have replaced the thermocouple, turn on the furnace and check to see if the pilot light stays lit. If your pilot light doesn't stay lit, it may be due to something blocking the thermocouple. You can try cleaning or replacing it, but if that doesn't work, you may need to call a professional.

Who to call when the pilot light goes out?

If after following the proper steps you still can't get your pilot light to stay lit, call an HVAC pro for a furnace repair.

How long does a thermocouple last?

How to Tell if You Have a Bad Thermocouple? Thermocouples can last up to 10 years if properly installed and maintained, while furnaces can last 15-20 years, although either may wear out sooner in multifamily units.

Will the pilot stay lit if the thermocouple is bad?

Nothing lasts forever, and when the thermocouple wears out, the pilot won't stay lit and your appliance won't work. The pilot can go out for a number of other reasons, however, so if you're having trouble getting the pilot to stay lit, the thermocouple may not be at fault.

Can I replace a thermocouple myself?

It's easy to replace, and a new one costs $5 to $10. Rather than trying to unfasten the thermocouple inside the water heater's burning chamber, it's easier to remove the whole burner and thermocouple assembly.

What would cause a pilot light to keep going out?

Gas Valve & Gas Supply Issues

The pilot light depends on a reliable source of gas or propane in order to stay lit. Any issues with the gas valve that supplies that gas to the flame, whether it be dirty or malfunctioning, can result in that flame going out.

Should the pilot light be touching the thermocouple?

The pilot flame should touch the thermocouple at a specific level. If the flame is blue and weak, and barely reaches the thermocouple, it needs to be stronger. If it extends well above the thermocouple, it's too strong.

How to clean a thermocouple on a gas heater?

Safe Methods of Cleaning Thermocouples in Furnaces

Begin by turning off the furnace and allowing it to cool. Carefully detach the thermocouple while ensuring the wires stay connected. Gently clean the tip with a soft cloth or fine abrasive pad to remove soot or debris buildup. Avoid using abrasive chemicals.

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