It's no secret that gas furnaces involve fire. The heat in your home comes from the combustion of natural gas inside the furnace's burner chamber. This process requires a specific amount of gas to enter the chamber, allowing the furnace to burn cleanly and efficiently. Too much or too little gas can cause severe problems or inefficient operation.
The gas valve regulates the flow of fuel to the burners. The valve remains closed most of the time but opens when the thermostat requests heat. A faulty gas valve can lead to numerous problems, so recognizing the signs and symptoms of failure can help you diagnose problems with your home's heating system.
Signs of Gas Valve Trouble
A faulty gas valve will fail in the closed position. This fail-safe design prevents uncontrolled gas from entering your furnace, which also means that a gas valve problem will prevent your furnace from producing any heat. In general, the symptoms of a gas valve failure are straightforward: the burners won't ignite because they aren't receiving gas.
If your furnace turns on and then turns off or runs for a while, it's likely that your gas valve isn't to blame.
Troubleshooting Furnace Gas Valves
Problems with your gas valve will typically fall into three categories:
- Faulty valves
- Faulty wiring
- Signaling issues
Modern furnaces use electromagnetic gas valves that wait for a signal from the control board before opening. The usual start-up sequence includes several safety checks before any gas enters the furnace, including confirmation that safety switches are in their correct positions and that the draft inducer motor is operating. Once the control board passes these steps, it signals the gas valve to open.
If the gas valve isn't opening, it's usually necessary to start with the valve itself and work backward. Typical diagnostic steps include listening for the sound of the valve opening and checking to confirm that the valve is receiving power. A valve that won't open even if it's receiving a 24v signal is most likely faulty.
The next potential culprit along the line towards the control board is the wiring itself. Since the valve requires a 24v signal to open, problems with the wiring can prevent the valve from receiving power. In this case, the furnace will request gas, and the valve can respond, but the wiring fails to carry the message successfully.
Problems with the control board can also prevent the gas valve from opening, but you'll usually need a professional to resolve these. Remember that working with gas lines is always dangerous, so if you suspect a problem with your gas valve, don't try to replace it yourself. Instead, rely on an HVAC technician for furnace repair services.
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