Easy DIY Fix: Gas Fireplace Won’t Stay Lit

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Troubleshooting any type of appliance, and especially gas appliances, can be dangerous. The following is only an educational overview of how gas fireplace components are checked. It is not intended to be a complete DIY diagnostic or to replace the support of a qualified technician. If you are having problems with your gas fireplace, we recommend you contact a reputable gas fireplace shop or plumber who can assist.

Whether its mounted in the wall or in a mantle, there’s nothing as relaxing as sitting with your loved one in front of your fireplace on a cold night at home talking about everything and anything. Unfortunately, it can be a real bummer when your gas fireplace won’t stay lit due to wear and tear of parts or improper maintenance.

When this happens, there’s no need to panic, as the possible cause of the problem might be something easily fixed without needing the help of a technician. Try the following DIY fix at home for a fireplace that won’t stay lit.

Before You Begin: Is Your Pilot Light Lit Inside Fireplace?

The first thing you should do when faced with fireplaces that won’t stay lit is to make sure your pilot light is lit. You might be amazed to find out that the most straightforward fix for this is to light your pilot. The pilot is typically located inside fireplaces on one side close to the wall. if you have gas logs it should be located in the same area as the logs

Pilot Light Color

Apart from your pilot being lit, the flame must stay a steady blue. Your pilot should be about 90 percent blue, with very little yellow. It should also be touching the surrounding sensors such as the thermocouple and thermopile. If the color of the flame turns yellow or red, it’s a sign of gas contamination.

The Fix: Pilot Light to Gas Fireplace Won’t Stay Lit

So you’ve checked your pilot light and even reset it, but still, it wont stay lit. 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.

Tools Needed

  • Digital multimeter
  • Fine-grit sandpaper
  • Stainless Steel Brush

What is the Difference Between a Thermocouple and a Thermopile?

The thermocouple more or less acts like a sensor for gas flow and supplies gas to the pilot light through the gas valve. The thermopile, on the other hand, opens up the gas valve when the fireplaces are turned on.

The Thermocouple and the Thermopile carry out a similar function of converting heat to electricity, but the thermopile generates more electrical current compared to the thermocouple.

Step 1. Check Your Thermopile Output with the TH/TP Contacts

Your thermopile output can be tested with a multimeter using the TH/TP Contacts to check the amount of electricity it’s producing. Before running the test, ensure that your pilot light has been on for two minutes or more, then switch off your fireplace.

Find your main gas control valve, and locate the thermopile sensor then find the Electric Contacts labeled TH/TP and TP respectively on the valve. You can use your manufacturer’s guide to locate these.

Take the multimeter leads, placing one on the TH/TP terminal and the other on the TP terminal.

The multimeter should read 300 millivolts or more. If it reads less than 300 millivolts, it may be cause that your gas fireplace wont function, therefore, you should replace it.

Diagnosing a Thermopile Problem

Just like the thermocouple, the thermopile can be read with a multimeter to check if it’s the cause of the problem. Three hundred millivolts or higher voltage is a sign of a good thermopile. A reading below 300 millivolts would require you to replace the thermopile.

Diagnosing a Thermocouple Problem

It’s always a good idea to test your thermocouple with a multimeter to rule out the possibility of it being the reason behind your gas fireplaces not staying lit. If your thermocouple is still in good condition, you should be able to read 25 millivolts of voltage or higher, but if it reads less than 25 millivolts, your thermocouple needs to be replaced.

Step 2. Don’t Replace Your Thermopile or Thermocouple Right Away

Due to the function of your thermocouple and thermopile, it’s only logical that they will build up carbon deposits from burning all the time. This build-up can very well limit their effectiveness. Although it’s cheap to replace both probes, it’s far cheaper to clean them first.

Step 3. Cleaning the Thermopile

To quickly clean your thermopile, turn off the gas supply. With the help of a stainless steel brush and fine-grit sandpaper, you can scrub off as much piled up soot as possible.

Step 4. Re-test the Cleaned Thermopile

When you’re satisfied with the way the thermopile looks, go ahead and re-ignite the pilot light. After a few minutes, turn off the fireplace and take another reading with the multimeter.

Step 5. Replace if Cleaning Did Not Work

After cleaning, should the pilot light still not stay lit, it is probably time to get new equipment. Take out the faulty thermocouple and thermopile and replace them with new ones.

Other Reasons for Gas Fireplace that Won’t Stay Lit

Checking your thermopile for a fault is a simple DIY solution as to why your gas fireplace wont function, but if the above steps don’t work you may need to call a technician to fix your issue. Apart from a faulty thermopile and thermocouple, other possible reasons include:

Incorrect Gas Service Pressure

If your gas pressure is not properly set, then gas fireplaces won’t stay lit. You can get a technician to help you make the necessary adjustments.

Faulty Gas Valve

Although not a common fault with gas fireplaces, just like every other component, it is subject to failure. When this happens, you should call a professional to get it changed quickly to avoid a fire incident.

Moisture in the Drip Loop

Another possible cause could be moisture in the gas line. This is capable of diluting the natural gas, making the light go off.

Clogged or Dirty Burner Ports

When your burner ports are clogged, the flame tends to be uneven and might possibly go off. Cleaning dirty burner ports from time to time could help solve the problem.

Cleaning and Proper Maintenence

Gas fireplace won't stay lit. Thermopile vs Thermocouple

Regardless of whether the fix worked or not proper gas fireplace maintenance will save you a lot of stress in the future and make sure your fireplace stays functioning. When the fireplace is clean and undergone proper maintenance, it burns evenly and prevents dirt from destroying its mechanisms. With a hand brush, rag, and vacuum cleaner, you can get your gas fireplace sparkling clean again.

Proper maintenance of your gas fireplace can help prevent issues with your fireplace such as trouble keeping the unit lit.



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