When something’s wrong with your HVAC system, one of the first places to check is your thermostat. Many models have a digital display that will reveal a specific numerical error code. This error code can be used to help diagnose the problem and speed up the troubleshooting and repair process for HVAC systems like your furnace.

This is even easier with smart thermostats like the Lennox iComfort model. Let’s review three serious error codes—411, 225 and 31—to learn what the problem is. We’ll also cover what steps your technician will take to fix the problem, and the possible costs to do so.

Lennox Thermostat iComfort Error Code 411

Error code 411 is an urgent priority to take care of. You’ll see this error code appear when the outdoor unit’s low-pressure switch malfunctions five times or more during one heating or cooling cycle. Since this error code includes the outdoor unit, it may be involved with your air conditioner. Every time the low-pressure switch opens incorrectly, the error count increases. Once it reaches five strikes, the thermostat immediately shuts down the outdoor unit. This is called a lockout and is a safety feature intended to prevent damage.

Fixing the Problem

A technician will check the system charge using several methods, as the issue may be with the switch’s power connections rather than the low-pressure switch on its own. Once the cause has been uncovered, technicians will reset the outdoor unit by putting it in test mode or by resetting low-voltage power. Once the issue is resolved, the error code should automatically disappear.

Estimated Repair Cost

Replacing a low-pressure shutoff switch may depend on the specific model of your outdoor unit. You could expect to pay anywhere from $200 to more than $600 depending on parts and air conditioning repair costs. The shutoff switch itself costs an average of $30 to $150.

Solving Error Code 225

Error code 225 is specific to your furnace, namely the high-pressure switch. This switch is a safety component that releases high pressure inside the furnace, such as when airflow is obstructed. When this error code appears, it means the pressure switch can’t close. Without consistent airflow and pressure, the furnace won’t perform as efficiently.

Fixing the Problem

The technician will watch the high-pressure switch to see how it functions. They’ll measure the pressure while it [attempts|tries} to close during a heating cycle as well as its standard operating pressure. If they recognize a problem, an obstruction impacting airflow is the most common culprit. There are a few places to look, such as the vent and combustion air inducer. Technicians will check both these components as well as the condensate drain to find the blockage.

Estimated Repair Cost

Because there are a few places to inspect before an obstruction can be found, labor costs should be considered when taking care of error code 225. Ultimately, the total cost of this furnace repair will depend on where the problem is located as well as how long it takes the technician to determine the source.

Solving Error Code 31

Seeing error code 31 on your thermostat means it hasn’t been able to communicate with your furnace for more than three minutes. Multiple components communicate with the thermostat, so you might see this error code when any of them malfunction or fail. Most of the time this can be traced back to an electrical issue, like frayed wiring or a loose connection.

Fixing the Problem

A technician can review all the connections and wiring of the communicating components of your furnace. They should test voltages and wiring ohms as particularly high resistance can result in a disconnection. With a special tool called a multimeter, technicians can find out where the disruption originated from. Sometimes this is the furnace’s float switch, a component that shuts off the furnace when the condensate drain pan is too full.

Estimated Repair Cost

With multiple possible causes, it can be difficult to determine the total repair costs of error code 31. Technicians will inspect the float switch to rule it out before systematically reviewing electrical wiring and connections. If the cause is damage or a failed component, replacement part costs should be included. You can expect to spend anywhere from $200 to more than $800 for higher-range models.