When something’s messing with your HVAC system, one of the first places to look is your thermostat. Many models use a digital display that will show 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 simpler with smart thermostats like the Lennox iComfort model. Let’s take a look at three serious error codes—411, 225 and 31—to find out what the problem is. We’ll also share what steps your technician will take to resolve 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 across one heating or cooling cycle. Since this error code involves the outdoor unit, it might be involved with your air conditioner. Each time the low-pressure switch opens incorrectly, the error count increases. Once it passes five strikes, the thermostat automatically switches down the outdoor unit. This is called a lockout and is a safety feature intended to minimize damage.

Fixing the Problem

A technician will test the system charge using several methods, as the issue may be with the switch’s power connections rather than the low-pressure switch itself. Once the cause has been found, technicians can reset the outdoor unit by placing it in test mode or by resetting low-voltage power. Once the issue is repaired, the error code should automatically clear.

Estimated Repair Cost

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

Lennox Thermostat iComfort Error Code 225

Error code 225 is specific to your furnace, namely the high-pressure switch. This switch is a safety component that releases excess pressure inside the furnace, such as when airflow is blocked. When this error code shows up, it means the pressure switch will not close. Without steady airflow and pressure, the furnace won’t run as efficiently.

Fixing the Problem

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

Estimated Repair Cost

Because there are several places to look 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.

Lennox Thermostat iComfort 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 find this error code when any of them malfunction or fail. Most of the time this can be traced back to an electrical issue, like old 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 will test voltages and wiring ohms as especially high resistance can lead to 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 down the furnace when the condensate drain pan is too full.

Estimated Repair Cost

With multiple possible causes, it may be difficult to estimate 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.