You’re likely sitting in a chilly house right now, hearing the inducer motor rev up only to have the system shut down before the burners even ignite. You might hear a rhythmic clicking or the blower fan running constantly without producing any heat. Don’t panic; this is a common protective measure. Most of the time, we can get this sorted with some basic troubleshooting and a few simple tools.
Symptoms of a Pressure Switch Cycle Lockout
The most obvious sign is the diagnostic LED on the control board blinking six times in a rapid red sequence, followed by a pause. Physically, you will notice the inducer fan (the small blower) starts spinning, but the igniter never glows and the gas valve never opens. Because the system has “locked out” after four failed attempts, the main blower fan may run continuously in an attempt to clear any unburned gas or cool the heat exchanger. You will feel cold air coming from your vents, and the thermostat will show that the system is “calling for heat” without any actual temperature rise in the home.
🛠️ Safety Precaution: High Voltage
Incorrect repairs can cause fire or injury. Always verify with the manufacturer’s manual.
Comprehensive Repair Guide
- Safety First – Power and Gas: Before you touch anything, flip the service switch on the side of the furnace to “Off” or shut down the dedicated breaker in your electrical panel. WARNING: Working on a live furnace exposes you to 120V current and moving parts. Ensure the power is verified off with your multimeter.
- Inspect the Vacuum Tubing: Open the cabinet and locate the small rubber hose running from the inducer motor to the circular pressure switch. Pull it off and inspect it for cracks, brittle ends, or water droplets inside. If there is water, blow it out; condensation buildup is a common cause of Error 6 in high-efficiency units.
- The “Paperclip Trick” (Cleaning the Port): Remove the hose from the inducer motor side. Take a small paperclip or a piece of stiff wire and gently poke it into the small plastic hole where the hose was attached. This clears out any “crud” or oxidation. I’ve fixed more “broken” furnaces with a paperclip than with a toolkit.
- Check the Flue Exhaust: Go outside and look at where your furnace vents. Ensure there isn’t a plastic bag stuck over it, snow blocking the pipe, or a beehive inside the rim. Any restriction here will prevent the pressure switch from closing.
- Test the Switch Continuity: Set your multimeter to Ohms (Ω). With the wires removed from the pressure switch and the furnace powered OFF, the switch should show “Open” (OL). Now, reconnect the wires, turn the power ON, and set the thermostat to call for heat. When the inducer motor reaches full speed, check for voltage across the switch or continuity. If the motor is running but the switch remains “Open,” and you’ve cleared the ports, the switch is likely defective and needs replacement.
- Inspect the Inducer Wheel: If the motor sounds like a “box of rocks” or is vibrating heavily, it may not be pulling enough vacuum. Use your nut driver to remove the motor and check the internal fins for damage or debris.
- Project Difficulty: Intermediate (Requires basic electrical testing)
- Estimated Time: 45 to 90 minutes
- Tools Needed: Phillips head screwdriver, 1/4″ nut driver, Digital Multimeter, small paperclip or stiff wire, and a flashlight.
- Estimated Cost: $0 (Cleaning/Adjustment) to $150 (Replacement Parts)
Technical Explanation of the Fault
The pressure switch is a safety watchdog. Its job is to ensure the inducer motor is creating enough vacuum to pull combustion gases out of the heat exchanger and vent them outside. If this vacuum isn’t strong enough, the furnace won’t fire because it risks leaking Carbon Monoxide into your home. Here is why it usually fails:
- Physical Blockages in the Venting: Over years of service, your exhaust pipes can become home to bird nests, dead rodents, or even ice buildup during extreme cold. If the air can’t move, the pressure switch won’t “make” (close), telling the board it’s unsafe to light the fire.
- Clogged Pressure Ports: This is the “mechanic’s secret.” There is a tiny hole (nipple) where the rubber vacuum hose connects to the inducer housing. Over time, oxidation or debris can plug this tiny hole. Even if the motor is working perfectly, the switch “feels” no vacuum because the hole is blocked.
- Inducer Motor Fatigue: The bearings in the inducer motor can wear down, or the internal fan wheel can become coated in grime. If the motor isn’t spinning at its rated RPM, it won’t generate the specific inches of water column (WC) pressure required to trip the switch.
- Diaphragm Failure: Inside the switch itself is a thin silicone membrane. Years of heat cycles can cause this membrane to stiffen or tear. When this happens, the switch becomes mechanically unresponsive to the vacuum.
How to Prevent Error 6 Red Flashes
The best way to handle an Error 6 is to never see it in the first place. First, **clean your pressure ports annually**. During your fall maintenance, just pop that hose off and make sure the port is clear. It takes ten seconds and saves a midnight service call.
Second, **install a protective screen** on your exterior vent terminations. Use a mesh that is wide enough not to restrict air but fine enough to keep out birds and squirrels. Finally, ensure your furnace is leveled correctly. York furnaces are sensitive to “settling”; if the unit tilts slightly forward, condensate water can pool in the inducer housing, blocking the pressure port and triggering a lockout.
Frequently Asked Questions
Q: Can I just jump the wires on the pressure switch to get heat tonight?
A: Absolutely not. Never bypass a safety switch. The pressure switch ensures that toxic combustion gases are being exhausted. If you bypass it and there is a blockage, you risk filling your home with Carbon Monoxide. It’s a life-safety device, not a suggestion.
Q: Why did the error happen 4 times before locking out?
A: York engineers designed the board to be “forgiving.” Sometimes a gust of wind can momentarily open a switch. By requiring four consecutive failures, the board confirms the issue is a persistent mechanical fault rather than a fluke environmental factor.
Q: How do I reset the Error 6 code?
A: Once you’ve performed the repair, you can usually reset the board by flipping the power switch off for 30 seconds and then back on. However, if the fault isn’t actually fixed, the furnace will simply attempt four more cycles and lock out again in about 10 minutes.