Choose the right setting for your Nest thermostat’s reversing valve

Important: This article applies to all smart thermostats in North America (NA), but doesn’t apply to thermostats in the European Union (EU).

Your Nest thermostat offers 2 main ways to activate the reversing valve: “Seasonal” or “Cyclical.” To help your thermostat’s heat pumps operate correctly and efficiently, choose the right reversing valve setting during setup. The setting you choose depends on your heat pump’s design. A correct thermostat setup can help you:

• Prevent common installation issues
• Improve your thermostat’s efficiency
• Reduce wear on the equipment
• Support comfort in your home

Learn the difference between Seasonal and Cyclical activation

When a heating or cooling cycle is running, the reversing valve switches based on the mode set on your thermostat. During a heating or cooling cycle, your thermostat activates or deactivates the reversing valve based on the set mode. For example, when your thermostat is running a heating cycle, where the Y1 and O/B wires are activated, it will deactivate Y1 once the target temperature is reached.

After a heating or cooling cycle, your thermostat manages the O/B wire that controls the reversing valve in different ways, depending on its configuration:

• Seasonal activation: Keeps O/B activated to prevent the valve from moving when it doesn’t need to.
• Cyclical activation: Deactivates O/B to reset the position of the reversing valves for the next cycle.

Your thermostat’s heat pump behavior may vary across different systems. Some behaviors of other units include:

• A loud swishing sound when the reversing valve switches.
• Air that blows of the opposite temperature if the reversing valve changes position at the end of a cycle.
• Continuing to heat or cool after the Y1 wire is deactivated if the O/B wire remains active.

Seasonal activation

Also referred to as “Seasonally” or “Seasonal,” this is the most common setting for many modern heat pumps. When Seasonal activation is enabled, the number of times the reversing valve switches is minimized.

Seasonal activation is the recommended setting for most heat pumps. This setting prevents the reversing valve from switching after every heating or cooling cycle, which can greatly reduce wear and tear. If your heat pump operates on Seasonal activation when it should be running on Cyclical activation, your thermostat might continue to:

• Heat after the heating cycle ends and the thermostat becomes idle, which could lead to overheating
• Cool after the cooling cycle ends and the thermostat becomes idle, which could lead to overcooling

Tip: If you experience any of these issues, you might be able to fix them once you change your reversing valve activation settings. If you’ve already changed your settings and performance issues persist, consult your HVAC equipment manual or contact a professional for help with adjusting the settings.

Cyclical activation

Also referred to as “Cyclically” or “Each cycle”. It suits heat pump models with reversing valves which are prone to getting stuck. When Cyclical activation is enabled, the reversing valve cycles back to a default position after each heating or cooling cycle ends.

Cyclical activation is needed for older heat pump models as the reversing valves tend to get stuck. However, the increased valve movement and switching can lead to more wear over time compared to Seasonal activation. If your heat pump operates on Cyclical activation when it should be running on Seasonal activation, there might be a:

• Loud swishing sound at the end of the heating or cooling cycle
• Brief burst of hot or cold air at the end of a heating or cooling cycle

Tip: If you experience any of these issues, you might be able to fix them once you change your reversing valve activation settings. If you’ve already changed your settings and performance issues persist, consult your HVAC equipment manual or contact a professional for help with adjusting the settings.

Change your reversing valve activation settings

Nest Learning Thermostat (4th gen) and Nest Learning Thermostat

1. Open the Google Home app .
2. Tap Home   Climate   your thermostat.
3. Tap Settings Thermostat Heat pump.
4. Change the activation setting.

Nest Learning Thermostat (3rd gen or earlier) and Thermostat E

1. On your thermostat, go to Settings .
2. Select Equipment Continue Continue.
3. Select Pro setup Continue.
   • Tip: You may find other questions based on your system. Continue through the flow until the screen displays a wiring diagram.
4. Select the Heat pump terminal.
5. Change the activation setting.