How to Detect Leaking Furnace Gas Valves

Someone working on hvac gas lines.

A leaky furnace valve is a dangerous situation that should be dealt with immediately. Fixing the leak will reduce the chances of a catastrophic fire and prevent carbon monoxide poisoning. From simple soap sprays to toxic gas detectors, here is a guide on how to find a leaking furnace gas valve.


Observation is one of the easiest ways to detect a gas leak. Apart from smell, look for cracks in the housing and any joints that look damaged or loose. You can use a flashlight and a mirror for hard-to-reach places. You can also check the color of the furnace flames. If you notice a change in hue, then it's possible you have a leaky valve somewhere.

Places to Look

Gas valve leaks usually occur around fittings and joints. It's possible, however, to damage straight pipes, though this is less likely under normal use. When looking for possible leaks, work your way from the pipes towards the furnace, ending the search at the pilot tube and burner.

Carbon Monoxide

A carbon monoxide detector.

Carbon monoxide is fortunately easy to detect in gas furnace leaks. Simply purchase a carbon monoxide detector and place it near the furnace. The device will alert you whenever it detects high levels of carbon monoxide. Just ensure the detector has full batteries and is located close to the furnace.

Soap Spray

If the valves look good and you can't smell any gas, try using a soap solution to detect leaks. Mix soap and water in a bottle and spray it liberally on the valves. A leaky valve will create bubbles in the solution. This method is very basic, but it's extremely effective in troubleshooting damaged valves.

Specialized Detectors

You can purchase special detectors that find leaks around gas furnaces. The only problem with these detectors is that they are not completely dependable and don't detect all leaks. They can, however, be incorporated into a larger system for finding leaks or used to confirm an existing leak.

Professional Service

An hvac professional working on a furnace.

If you can't confirm a leak, it's always a good idea to call in a professional for a second opinion. Not only will they find the problem, but they can also fix it straight away. The only downside to calling the pros is the price, especially if they fail to find anything wrong with the system.

Combine Techniques

If you're having trouble finding the leak but can smell the gas, try using a combination of methods. None of these techniques will catch all the leaks if used by themselves but combining two or more will give you a better chance of solving the problem. Using more methods also ensures that you don't accidentally miss a leak without properly fixing it.


Once you discover a leaky gas valve, it's important that you shut off the furnace. This will help decrease the chances of an accident. If you detect the presence of carbon monoxide, make sure the room is properly ventilated before attempting a repair. Turn everything back on after you fix the broken valve and run through the checks one more time to rule out any additional leaks.