When something’s messing with your HVAC system, one of the first places to check is your thermostat. Many models have a digital display that will show a specific numerical error code. This error code can be used to help diagnose the problem and streamline 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 take a look at three serious error codes—411, 225 and 31—to learn what the problem is. We’ll also share what steps your technician will take to fix the problem, and the possible costs to do so.

Solving 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 throughout 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 turns down the outdoor unit. This is known as a lockout and is a safety feature intended to reduce damage.

Fixing the Problem

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

Estimated Repair Cost

Swapping out a low-pressure shutoff switch might depend on the specific model of your outdoor unit. You may 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.

Clearing Error Code 225

Error code 225 is specific to your furnace, particularly the high-pressure switch. This switch is a safety component that releases high 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 consistent airflow and pressure, the furnace won’t work as efficiently.

Fixing the Problem

The technician will check the high-pressure switch to determine how it functions. They’ll measure the pressure while it [attempts|tries} to close during a heating cycle as well as its general operating pressure. If they find a problem, an obstruction stopping airflow is the most likely culprit. There are a few places to check, 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 check before an obstruction can be found, labor costs should be considered when taking care of error code 225. Ultimately, the final cost of this furnace repair will depend on where the problem is located as well as how long it takes the technician to identify the source.

Resolving 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. Several components communicate with the thermostat, so you may see this error code when any of them malfunction or fail. Most of the time this can be traced back to an electrical problem, like bad wiring or a loose connection.

Fixing the Problem

A technician can inspect all the connections and wiring of the communicating components of your furnace. They should test voltages and wiring ohms since 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 overflowing.

Estimated Repair Cost

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