Heating IssuesFurnace Gas Valve Troubleshooting: 6 Common Issues to Check and How to Fix Them

Your gas furnace has been good to you every winter in your Sacramento home, it has been the most reliable means of efficient home heating. But what happens when it fails to ignite and needs a quick fix so you’re not left cold and frustrated? Of course when your gas furnace fails to ignite, you can call a local technician for Sacramento HVAC service, but this often comes at a costly price.

Alpha Mechanical professionals would love to come out and service your furnace, however, we also value your time and money and believe minor problems can be handled at home. Before we get into how to repair gas valve on furnace, let’s break down the issue and try to solve it following these heater gas valve troubleshooting steps.

Before troubleshooting your gas valve, let’s be sure that:

1. The furnace gas valve on off switch has to be in the ON position to ensure it is getting power. The switch should look similar to a light switch and will be located on or near the furnace.
2. The handle/knob for the gas valve runs parallel to the line when in the ON position, double check that it is in this position.
3. The thermostat is set to “Heat”

Gas Furnace Sequence:

Thermostat calls for heat → Inducer Motor Starts → Inducer pressure switch triggers → Ignitor turns on → Gas Valve opens → Flame Sensor sense flame → Blower turns on

1. The first thing will turn on is the inducer motor when 120 volts are administered through the wires coming from the control board which starts the inducer motor for up to 60 seconds before anything else is activated.
2. Once that is running a safety device called a pressure switch will come on once the diaphragm recognizes the suction from the inducer motor.
3. After the safety device signal reaches the control board, high voltage is sent to the ignitor through a hot surface ignitor/spark ignitor.
4. The gas coming from the utility company or the propane tank in the back yard is free to flow to the ignitor and 24 volts is given to the gas valve. The gas valve is what regulates the flow of gas and that’s why it is important.
5. The flame sensor recognizes whether the flame is burning correctly or not. The rod (which should be annually cleaned) will heat up and send a millivolt signal down its ceramic base and onto the control board. A specific amount of gas can be allowed to pass through the manifold and on to the burners safely which is typically a standard 3.5” water column (wc) although some vary.

Furnaces differ sometimes by brand so be sure to check your furnace installation service guide for your system specifics. This is something you don’t want to get wrong.
The gas valve is adjustable and usually the installer of the equipment will dial in the outlet pressures on the start up. Because the gas valve manufacturer-Emerson, White-Rodgers, Honeywell, and other valve makers will usually have it pre-set to that 3.5” wc, we don’t want to assume it’s been done or that you have a standard system. In some cases the valve might not have been installed correctly especially if you are having gas valve related issues with your furnace.

Once you have checked that 24 volts is being received on the control board, the issue may be downstream of the voltage. If the voltage is correct but you are not hearing the slight clicking noise the internal valve is supposed to make, it is possible that you have a bad gas valve. If your furnace gas valve not opening, either the electronic solenoid attached to the gas valve (printed circuit board) isn’t telling the valve to open OR that gas valve is stuck somehow. Some websites will recommend banging on the gas valve with a wrench, however, this is extremely dangerous as gas is not something to mess around with. If something is wrong with the internal components of the gas valve, it should be replaced. Remember that gas valve repair and gas valve replacement can only be done by the manufacturer of the valve or someone certified by the gas valve manufacturer. Be sure to check the gas pressure on the new valve once it’s been replaced just to be safe.

1. Gas Valve Wires

Cracked or frayed wires could indicate that you need to replace your furnace due to its age or that something has scorched the wire. If the wire looks disabled in any way, replace it and continue your diagnosis. If it is time for you to look for a furnace replacement company, look no further.

2. Gas Valve Coil

You can check the coil at the gas valve and it’s resistance using your two-meter leads on each terminal. If the reading says OL, you have a bad coil.

3. Ignition Source

Turn off your furnace before completely this step
There are two ways a furnace ignites the gas air mixture that comes into it; it does so either through the pilot light or electronic furnace ignition.

• • If your furnace has a standard pilot light, you will be able to see it by looking underneath your furnace at the tray where the burners are, the pilot light is located to one side of this tray just barely above it usually. A furnace pilot light is a small flame that is constantly on burning a small amount of gas persistently which makes it easy to identify even if your furnace is off. If you do not see a small flame, carefully take a long lighter/match to try to light it again.
  • If your furnace has an electronic furnace ignition, it has a safer system and is not using a constant amount of gas, when it is off, it’s off. Underneath your furnace, the electronic ignition should be in the same place as the pilot light.
  • To test if this is the source of your problem, look under your furnace after trying to start it up and see if it’s glowing. You will also hear a clicking, however, if you are hearing a persistent/repeated clicking noise, this usually means your ignitor is not coming on. If this issue comes up, turn off your furnace and give it some time before attempting to fix it. Once you’re ready, very gently reach in and clean the igniter and the area around it, emphasis on gently because the ignitor tip is very fragile. Cleaning the ignitor can clear up any carbon build up that may be preventing it from coming on.
  • If your furnace is not lighting, it could also be a sign that your heat exchanger is damaged. There are several indicators that your heat exchanger could be the issue such as loud sounds coming from the unit, soot build up or furnace cracks and corrosion.

4. Inconsistent flame

The flame might be coming on for a few seconds but then shutting off. To check and solve this issue you can see if the voltage is off or the gas pressure is low to the valve by putting a “T” (fitting in line with the hose) to connect to your manometer. Check the input and output side to see if the pressure is decreased on either side of the valve. Another reason for inconsistent flame is that the flame sensor or gas furnace regulator may not be sensing the flame which would signal the gas valve to either shut off or for the gas to keep running when it’s not supposed to.

5. Safety trip

• If the direction of the flame isn’t going straight into the hollow metal heat exchanger, a safety trip will be triggered. If a small part of the flame is veering to the left or right, this is an indicator that something needs fixing. One thing to keep in mind is sometimes rust can build up on the crossover channels but can be safely cleaned with a wire brush. Clean the end of the burner assembly closest to the heat exchanger. Then place the burner correctly into the channel and see if that fixes it.
• Another safety trip that can trigger the system to shut off after booting up first is the high limit switch. If the furnace runs for a few minutes, then shuts off, the inside of the furnace might be getting too hot. Check whether the evaporator coil is dirty.
• The other reason the high limit could open is the blower motor speed could be set too low. To reset your high limit switch, check your installation guide as a reference, this should tell you where the settings are supposed to be.

6. Ductwork

If the return ducts are crushed, then the furnace may be suffocating due to inability for air to flow. See that the duct is perfectly round and the fuel around it doesn’t look questionable, otherwise, this could be your problem. Another airflow issue that could be present is a dirty air filter, be sure to change the filters once every 3 months in your furnace.

At Alpha Mechanical our goal is to leave you with lasting appliances and tips to solve your minor conveniences leaving you with peace of mind and comfort in your homes. We never seek to upsell unnecessary equipment or rip off our customers financially when it comes to their HVAC units. Our technicians can break down what’s needed for your heating or air systems to run properly again, the cost of the repair and equipment, and what would be most efficient for your home.

We even offer coupons and financing through partnered banks. We can always inform our customers before completing the job so that you’re in the know of the work that needs to be done, not leaving you shocked with a price you did not expect. Communication is key to quality service for our customers, giving them prime service is our utmost priority.

Before the cold season for Sacramento settles in, we recommend getting your furnace routine annual check completed checking over the entire system making sure it’s running smoothly and that all of its parts have been cleaned. Heater gas valve troubleshooting may seem daunting to some and can be a dangerous thing to attempt with little experience, it’s best to call an HVAC professional when you are unsure. Sometimes the repair is as simple as replacing wires or coils, but other times it gets into the structure of the furnace itself. Be sure to follow each step carefully and call a specialist when you are coming to a dead end.