Furnace Not Getting Gas

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Quick answer
Confirm the symptom
Tools and prep
Step-by-step troubleshooting
Common causes table
Parts matching
When to call a pro
FAQ
Related guides

Quick answer

If your furnace isn't getting gas, first check the gas supply valve and ensure it's fully open. Verify the pilot light is lit and the thermocouple is functioning. If the gas pressure is low or the gas valve is faulty, contact a professional HVAC technician.

Confirm the symptom

Furnace won't start at all
No gas smell when attempting to start
Pilot light won't stay lit
Gas valve makes a clicking sound but no gas flows
Furnace blower runs but no heat

Tools and prep

Gas leak detector or soapy water solution
Screwdrivers (flathead and Phillips)
Flashlight
Owner's manual for the furnace
Wrench for gas valves
Safety goggles
Turn off the furnace power at the thermostat or circuit breaker
Ensure the area is well-ventilated

Step-by-step troubleshooting

Check Gas Supply Valve
Do: Locate the gas supply valve near the furnace and ensure it's fully open.
Observe: Valve handle is parallel to the gas line.
Means: Gas is allowed to flow to the furnace.
Next: If the valve is closed or partially closed, open it and try starting the furnace again.
Verify Gas Supply
Do: Check if other gas appliances in the home are working.
Observe: Other gas appliances (e.g., water heater, stove) are operational.
Means: Gas supply to the house is active.
Next: If other appliances aren't working, contact your gas provider.
Check for Gas Leaks
Do: Apply soapy water to gas lines and connections.
Observe: Bubbles form at a leak site.
Means: Gas leak is present and needs repair.
Next: If a leak is detected, shut off the gas supply and call a professional.
Inspect Pilot Light
Do: Look at the pilot light assembly to see if it's lit.
Observe: Pilot light is out or flickering.
Means: Pilot light may not be igniting the gas.
Next: If the pilot light is out, follow the manufacturer's instructions to relight it.
Test Thermocouple
Do: Use a multimeter to test the thermocoupler's voltage.
Observe: Voltage reading is below 25 millivolts.
Means: Thermocouple is faulty and needs replacement.
Next: Replace the thermocouple if it's not generating sufficient voltage.
Check Gas Pressure
Do: Use a manometer to measure the gas pressure at the furnace.
Observe: Pressure is below the manufacturer's specifications.
Means: Low gas pressure may prevent proper operation.
Next: Adjust the pressure or consult a professional if adjustments don't help.
Examine Gas Valve
Do: Inspect the gas valve for signs of damage or blockage.
Means: Gas valve is blocked or damaged.
Next: Clean the valve or replace it if necessary.
Review Error Codes
Do: Check the furnace control board for any error codes.
Observe: Error code related to gas supply or ignition.
Means: Specific issue identified by the furnace's diagnostics.
Next: Refer to the owner's manual to interpret the error code and take appropriate action.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Gas Supply Valve Closed The main gas valve to the furnace is shut off, preventing gas flow.	Common	Easy	None
Gas Leak in Lines A leak in the gas line or connections reduces or stops gas flow.	Sometimes	Medium	Gas line repair kit
Faulty Thermocouple A malfunctioning thermocouple fails to send a signal to the gas valve to open.	Common	Easy–Medium	Thermocouple
Low Gas Pressure Insufficient gas pressure from the utility company or a clogged gas line.	Sometimes	Hard	Gas pressure regulator
Blocked Gas Valve Debris or rust inside the gas valve prevents gas from flowing.	Sometimes	Medium	Gas valve
Faulty Ignition System An electronic ignition system failure prevents gas from being ignited.	Sometimes	Medium	Ignition module
Gas Line Blockage A blockage in the gas line due to debris or corrosion.	Rare	Hard	Gas line cleaning or replacement
Faulty Gas Valve Solenoid The solenoid inside the gas valve is not opening to allow gas flow.	Rare	Hard	Gas valve solenoid

Parts matching

Common parts needed to fix a furnace not getting gas include:

Gas supply valve
Thermocouple
Gas pressure regulator
Gas valve
Ignition module
Gas line repair kit

Always refer to your furnace's owner's manual to confirm the correct part numbers and specifications before purchasing replacements.

When to call a professional

You detect a gas leak (smell of gas or bubbles from soapy water test)
You're unsure about handling gas lines or pressure adjustments
The furnace error codes indicate a complex issue beyond basic troubleshooting
The gas supply valve is frozen or damaged
You hear a gas smell after attempting repairs
The furnace still doesn't work after checking all basic components

FAQ

Why won't my furnace start even though the gas valve is open?

The gas valve may be partially blocked, or there could be an issue with the ignition system or thermocouple. Check for error codes and inspect the pilot light or electronic ignition.

Can a bad thermocouple prevent gas from flowing?

Yes, a faulty thermocouple won't send the signal to the gas valve to open, so the gas won't flow even if the valve is open.

How do I know if there's a gas leak near the furnace?

Apply soapy water to the gas lines and connections. If bubbles form, there's a leak. You may also smell gas or hear a hissing sound.

What should I do if the pilot light won't stay lit?

Check the thermocouple positioning and ensure it's generating enough voltage. If it's faulty, replace it. Also, ensure the pilot light is properly adjusted.

Why is my furnace getting gas but not igniting?

The ignition system (pilot light or electronic ignition) may be faulty. Check the thermocouple, ignition module, or spark electrode for issues.

Can low gas pressure affect furnace performance?

Yes, low gas pressure can prevent the furnace from starting or cause it to run inefficiently. Check the gas pressure with a manometer and contact your gas provider if it's below specifications.