Standing Pilot Troubleshooting Tips
Disclaimer: Due to the dangerous nature of gas units (sometimes explosive if serviced incorrectly), we highly recommend hiring a qualified expert with the experience and tools to help troubleshoot and install replacement parts safely. This information is not intended as a comprehensive guide. If you choose to perform any troubleshooting or replacement yourself, you do so at your own risk.
A standing pilot stove or fireplace uses a thermocouple and/or thermopile to sense temperature and control fireplace operation. The pilot flame is created by pressing and holding a piezo igniter button located on or near the valve, and the pilot light remains lit all the time. This type of system is popular because it does not require electricity to operate, so you don’t have to worry about losing heat during severe weather in the event of a power outage.
Watch an example of standing pilot in action with this video from Napoleon Fireplaces:
What is a thermocouple?
A thermocouple is an insulated copper tube containing 2 wires made of different kinds of metal that are joined at each end. When the pointy thermocouple tip senses heat from the pilot flame, the heat splits and travels down the 2 wires, creating a low-voltage electric current when the wires rejoin. This is measured in millivolts. The electric signal from the thermocouple tells the gas valve to send gas to support the pilot flame.
Thermocouples are used in stoves and fireplaces to sense temperature and signal that the pilot light remains lit. If the pilot light goes out, the thermocouple will cut off the flow of gas from the valve as a safety feature.
What is a Thermopile?
A thermopile is a fat, round probe made of several thermocouples bundled together. These thermocouples work together to generate a stronger electric current. Thermopiles offer greater accuracy in sensing temperature due to their increased sensitivity to temperature than a single thermocouple.
Thermopiles are used in gas stoves and fireplaces to generate a low voltage of electricity that is sent to open the gas valve and allow gas to flow into the burner. Thermopiles produce enough power to allow temperature control with a thermostat (such as a remote or wall thermostat).
Tools you may need:
- Multimeter that can read millivolts
- Fine sandpaper and/or extra fine grit steel wool
- Jumper wire with spade clips
Common Standing Pilot Troubleshooting
The most common issue experienced with a gas fireplace is trouble turning it on. If you feel qualified to troubleshoot your own gas fireplace there are a few simple ways to narrow down the source of the problem before scheduling a service call. Remember, gas appliances are very dangerous if serviced incorrectly, so be sure to hire an expert for any tests or repairs that are beyond your abilities.
Troubleshooting a Faulty Pilot Light
Without a pilot light, the entire fireplace will not operate. Sometimes the pilot may have blown out. The solution may be as simple as relighting the pilot according to the fireplace manufacturer instructions. Refer to the owner’s manual for your fireplace to find instructions specific to your exact model.
Another simple fix is to double check the fuel supply. Without fuel, the fireplace will never light. Make sure that the manual gas valve that allows gas into the fireplace is open and if that there is fuel in the tank or gas supply line into your fireplace. Once you verify the proper fuel supply, ask these 3 questions to narrow down issues with the pilot light:
1. Does the pilot spark?
When the piezo igniter button is pressed and held down, you should hear a “click” as the igniter sends a spark to the igniter electrode. No spark? First, make sure the electrode wire is securely connected to the piezo. Look for a pinched or broken igniter wire. Check the porcelain base of the electrode for cracks or damage. If all these things check out, then you may need to replace the piezo igniter.
2. Does the pilot light?
If you see the spark from the igniter, but the pilot still doesn’t light, there is probably an issue with the flow of gas. Can you smell the presence of gas in the firebox? Check the pilot orifice and pilot tube for any blockage that could be interrupting the flow of gas from the control valve to the pilot hood.
If these tests do not resolve the problem, then you may need to consult an expert who can check for air in the gas lines and verify proper gas inlet supply. A qualified technician will have special gauges to measure the gas flow pressure and verify whether the gas valve needs to be replaced.
3. Does the pilot go out?
If the pilot lights but immediately goes out again, you most likely have a faulty thermocouple. Try re-lighting the pilot again. If it does not remain lit, you can clean and test the thermocouple.
1) First, shut off the flow of gas at the knob on the gas valve and at the manual shutoff valve that allows gas into the fireplace.
2) Check the thermocouple tip in the pilot assembly for carbon buildup. You can try cleaning this tip with extra fine steel wool and/or fine grit sandpaper.
3) Set your multimeter to measure millivoltage.
4) Connect one of the multimeter leads to the copper tube of the thermocouple and the other lead should connect to the end of the thermocouple where it screws into the gas valve.
5) Use a lighter or small butane torch to heat the tip of the thermocouple for about 30 seconds.
6) The multimeter should read between 25-30 millivolts. If the thermocouple produces less than 25 millivolts it should be replaced.
If none of these remedies resolve the issue, we recommend hiring an expert to check out the fireplace.
Troubleshooting a Faulty Burner
If the pilot burns just fine, but the fireplace still won’t work properly then the burner and gas valve are the next areas to inspect. A standing pilot gas valve, referred to as millivolt, will have 3 electrical contacts labeled TH, TP, and TH/TP.
TH – stands for thermostat (such as a wall switch, thermostat, or remote)
TP – stands for thermopile (The fat probe in the pilot assembly)
TH/TP – connects to both the thermostat and the thermopile
Does the burner come on?
Thermostat - The first place to start when the burner does not come on is the thermostat. This could be a wall switch, a wall thermostat, or possibly a remote. Is the thermostat set properly to call for heat? Double check the wiring for any loose or broken connections, especially the terminals on the gas valve.
Thermopile – The thermopile uses the heat from the pilot flame to generate a millivolt signal telling the gas valve to send gas to the burner. The thermopile ends should connect to the TP and TH/TP terminals on the valve. Visually inspect the thermopile probe in the pilot assembly for carbon buildup. You can try cleaning the thermopile with extra fine steel wool and/or fine grit sandpaper. You can also test the thermopile performance with a multimeter.
Voltage Test #1
1) First, make sure that the pilot light has been burning for at least 2 minutes and that the thermostat or wall switch is turned off.
2) Set the multimeter to measure millivoltage.
3) Connect the leads of the multimeter to each end of the thermopile wires where they connect to the valve.
4) The multimeter should read between 300 -750 millivolts. If the thermopile produces less than 300 millivolts it should be replaced.
Valve Operator Heads – If the thermopile generates the correct voltage, check the terminals of the valve with the multimeter.
Voltage Test #2
1) Make sure that the pilot light has been burning for at least 3 minutes.
2) Place a jumper wire between the “TH/TP” and “TH” terminals of the valve operator head.
3) Set the multimeter to measure DC
4) Connect the leads to the “TH/TP” and “TP” terminals of the valve operator head.
5) The multimeter should read 225 millivolts or higher. If the reading is less than 225, then the gas control valve needs to be replaced.
Thermostat Circuit – If the fireplace still does not operate correctly, the thermostat circuit should be tested for continuity.
Thermostat Continuity Test
1) Remove the thermostat circuit wires from the TH/TP and TH terminals and connect the leads of your multimeter to each wire.
2) Set the multimeter to measure ohms (Ω).
3) Turn the rocker switch to the ON position to make sure the thermostat contacts are closed and complete the circuit. If the multimeter measures no resistance, then there is no continuity. The thermostat wires or switch should be replaced.
Is the proper burner flame present?
If the flame is too low or too high, verify that the regulator on the gas control valve and the burner orifice(s) are correct for the type of gas your fireplace uses. Natural gas and liquid propane require different ratios of air to fuel, so it is extremely important to use the correct regulator and orifices are installed. If this does not resolve the problem, you should consult a local technician with the tools and expertise to test the incoming and outgoing gas pressure. A qualified technician will also inspect the burner tube for blockage. They will be able to perform detailed diagnostics to advise whether the valve or burner needs to be replaced.
Strange Smells – may indicate the fireplace and or chimney pipe is due for a cleaning. Refer to the owner’s manual for a recommended cleaning and maintenance schedule. Take care when cleaning not to damage the fragile logs. Excess dust, dirt, and soot should be addressed by an expert. If you notice the smell of gas or melting wires, immediately discontinue use of the fireplace until a trained professional can take a detailed look.
Strange Sounds – while some sounds may be normal for your stove or fireplace, any new sounds that occur with operation issues should not be ignored. A poorly adjusted pilot flame or dirty burners can make a low, rumbling sound. Some units utilize an optional convection blower to boost heat distribution into the room. Convection blowers may develop a high-pitched squealing sound indicating the bearings have worn out and the blower is ready to be replaced.
Lots of Soot – If the oxygen ratio in the fireplace is too high or too low while operating it could create excessive creosote buildup. This could indicate that the air setting needs to be adjusted or there could be an obstruction, such as leaves or a bird’s nest, blocking the flue pipe. In this case, we recommend hiring a qualified technician to inspect and clean the fireplace because they will have the tools to adjust air settings and identify potential hazards.
Maintaining Your Gas Fireplace
Gas fireplaces should be professionally cleaned and inspected each year. This typically includes cleaning the burners and pilot assembly, checking safety systems, testing the ignition system, and inspecting the flue for creosote, blockage, or leaks. Following the recommended maintenance schedule ensures safe and reliable fireplace operation throughout the heating season.