3 Reasons Why Wall Heater Pilot Light Won’t Light?

Gas wall heaters are a little different from traditional gas furnaces. Although the working principle is the same, wall furnaces are slightly modified for wall installation. They are also improved to operate safely from the wall.

For these reasons, lighting a gas wall furnace is slightly different from traditional furnaces. Similarly, troubleshooting a malfunctioning ignition system on a wall furnace may be a little different. Nevertheless, it’s still a simple DIY process that doesn’t necessarily require professional intervention. 

The guide focuses on troubleshooting a troublesome wall heater pilot that won’t stay lit. What could be the problem, and what can you do about it? 

The Role of the Pilot Light System

Perhaps we should begin by explaining the role of the pilot system. The pilot light is the heart of the furnace’s ignition system. Without the pilot light, the burners cannot ignite. Thus there can be no heat. It also means that if the pilot light fails, you can forget about heating. 

When you turn on the gas heater, the valve releases gas to the burner, ultimately lighting the stove. However, this is as straightforward a process as you’d think. 

Why? Because there’s a real risk of the pilot delivering gas to the vent without lighting up. If this happens, gas will collect inside the chamber, creating a risk of explosion. 

Manufacturers solve this problem by providing a small valve on the pilot tube to manage the gas flow. This valve has a thermocouple located outside the pilot flame tube, generating electric power from heat. This thermocouple uses electromagnetic energy to close and open the gas valve on the pilot light, thereby controlling gas flow to the burner. 

As soon as the pilot flame lights, the thermocouple heats up gradually, generating enough electricity to stay open. But as soon as the flame goes out, the thermocouple closes, shutting the pilot gas valve simultaneously and the burners within seconds. Thus, the heating goes off. 

When Your Gas Wall Heater’s Pilot Light Won’t Stay Lit

As you can see, the furnace’s ignition system is an extremely delicate arrangement that can be compromised at the slightest sign of trouble. Even a small defect that affects the thermocouple for a second can cause the pilot light and the furnace itself to go off. 

If you keep lighting the pilot light and it keeps going off, you should check for the following three possible issues;

#1: Gas Supply Issues 

The first thing you want to check is the gas supply. Do you have enough gas in your lines? If so, is the gas reaching the heater? Above all, is it reaching the pilot system? Let’s address the three one by one.

  • Do you have gas?

The answer here will depend on the type of gas you use. For example, if you use a propane heater, you can check the tank manually to determine whether the tank has run empty. If it’s too low, arrange for a refill. However, if you use natural gas, you may need to contact your supplier to find out if they’re experiencing issues. If so, ask when the issues might be resolved.

  • Is the gas reaching the furnace?

If you find that you have gas, the next step is to confirm whether it’s reaching the wall heater. Sometimes you may blame the pilot system or even your heater when the appliance isn’t even receiving gas in the first place. Perhaps you have a leak that’s significantly affecting gas pressure. Or maybe the lines are blocked. It’s also possible that the gas valve is closed. You want to rule out all these. 

  • Is gas reaching the pilot light?

 Finally, gas may reach the wall heater but fail to reach the pilot light? Why? Because of a blockage within the furnace – or leaks. The most tell-tale sign that gas is reaching your furnace but not the pilot is when you hear a spark when you light the furnace, but nothing follows. It may be a sign of a damaged pilot system.  

#2: Blocked Pilot Tube 

If you’ve verified that gas is reaching the pilot system, but the pilot light still won’t stay lit, the next place to look is the pilot system itself. And the first thing to check is whether the pilot system is blocked. 

Gas furnace systems aren’t the cleanest of appliances. No matter how hard you try, it’s impossible to keep them spotless. You’ll always find dirt buildup around the surfaces. Carbon residue is also very common. These elements can get to the pilot system and partially or fully block the tube through which gas comes out. 

The good news is that you can check the area manually for dirt buildup. Better still, you can clean the area yourself to avoid an expensive service call. Here’s how to clean your wall gas furnace;

  1. Turn off the power: Shut off the electricity supply to the furnace at the circuit breaker. This will shut off both the furnace and blower. 
  2. Turn off the gas: Locate the supply line next to the furnace. It will have a cutoff valve. Rotate the valve to an “OFF” position. You can also use the gas meter. 
  3. Shut off the gas control valve: Open the access panel and reach the gas control valve. The access panel is typically located at the bottom of the furnace and held shut using screws. Once you locate it, shut off the gas control valve. 
  4. Find the pilot: The pilot system is located in the access panel. Follow the gas line from the control valve until you arrive at the end of the pilot. Wipe it with an emery cloth. Wipe the thermocouple too. 
  5. Scrap out the dirt: Insert the end of a straightened paperclip into the opening at the end of the pilot to remove any ash or debris. 
  6. Turn ON the controls: Start with the gas control valve. Then turn on the gas on the furnace and finish by turning the circuit breaker ON.
  7. Test the pilot and finish up: Push the gas control knob to “Pilot” and light the pilot while holding down the knob. Then slowly release the knob.

If it was a dirt buildup issue, it should now work. If so, rotate the gas control valve “ON” and close the access panel. 

#3: Faulty Thermocouple 

Finally, if you’ve cleaned the pilot system, but the problem persists, you likely have an issue with the thermocouple (also popular as the flame sensor). 

You may suspect the thermocouple if you see that it’s discolored, cracked, or has pinholes. Signs of wear and corrosion, such as missing insulation and bare wires, may also point to damage. However, it’s best to test it before making conclusions. The good news is that you can diagnose the thermocouple yourself. 

But you need to remove it first. Before you begin, make sure to turn off the gas supply and shut off the electricity. Then proceed as follows;

  1. Remove the thermocouple by unscrewing the copper lead and connection nut. Then remove the bracket nuts. 
  2. Place the tip of the thermocouple in a flame and wait until it gets very hot. You may need to wait several seconds.
  3. Attach the leads from the ohmmeter to the thermocouple. The first lead goes to the thermocouple body/side, while the other goes to the end of the thermocouple that sits inside the pilot light. 
  4. Take the reading on your meter. A working thermocouple should read 25-30 ohms. If it’s below 25 ohms, it’s time to replace it. 

The three steps above should be enough to troubleshoot a wall furnace pilot that won’t stay lit. If the pilot doesn’t light at all or lights, but the burners don’t respond, you have a different problem, perhaps a tripped limit switch.