Overview

If your Mysa for Central HVAC thermostat reboots or shuts off unexpectedly while cooling, the issue could be caused by a float switch. This safety device is designed to prevent water damage—but when triggered, it can cut power to your HVAC system and thermostat. In this article, we’ll explain what a float switch does, why it causes power loss, and how to troubleshoot the issue.

What Is a Float Switch?

When your air conditioner runs, it doesn’t just cool your home—it also removes moisture from the air. That moisture collects in a drain pan located beneath the evaporator coil. If the drain line becomes clogged, water can build up and overflow, potentially causing damage.

To prevent this, many HVAC systems include a float switch—a water sensor that monitors the level in the drain pan. If the water rises too high, the float switch cuts power to the HVAC system and thermostat to prevent flooding.

Common float switch setups include:

• Standard float switch in the internal drain pan

• External float switch used with a secondary drain pan

• Condensate pump with built-in float switch (used when water can't drain by gravity)

How a Float Switch Affects Mysa

When the float switch is triggered, it interrupts the 24V power signal sent from the HVAC system to your Mysa thermostat. This causes the thermostat to lose power and reboot.

You might experience:

• Frequent thermostat reboots during cooling

• System not reaching the cooling setpoint

• Thermostat shutting off when the AC turns on

These issues are most common during the summer months, especially in warmer climates where the system runs for long periods.

Diagnosing a Float Switch Issue

If you're unsure whether a float switch is the cause of power loss, look for clues in your Mysa thermostat's behavior or runtime data.

Key signs to look for:

• Reboots occur during or shortly after cooling begins

• Cooling was running before Mysa went offline

• Indoor temperature decreases once Mysa comes back online

• Thermostat stays online during idle periods

These patterns strongly suggest the thermostat is losing power due to an HVAC system shutdown—most likely from a triggered float switch.

Example

If your cooling setpoint is 77.5°F and the room reaches 78°F, cooling should activate.
If the thermostat shuts off shortly after and comes back online showing 77.8°F, this indicates cooling began but was interrupted.

How to Fix or Confirm the Issue

For Homeowners:

• Inspect the drain pan for standing water.

• Check the condensate line for clogs.

• Test the condensate pump (if applicable) to ensure it’s working.

• Temporarily set the system to OFF to prevent further reboots while troubleshooting.

If you’re unable to access or inspect components safely, we recommend contacting a licensed HVAC technician.

Summary

A float switch is a safety device that protects your home from water damage, but when triggered, it cuts power to both your HVAC system and your Mysa thermostat. This can cause Mysa to reboot or appear unresponsive during cooling calls.

The most common causes include:

• Clogged drain lines

• Standing water in the drain pan

• Faulty or stuck condensate pump

✅ Start by checking for water buildup or clogs. If you're unsure or can’t access your system, contact an HVAC professional for help.

If you need assistance reviewing your runtime data or confirming whether a float switch is involved, our Mysa Support Team is here to help.