Fujitsu VRF Thermostats: How Heat Pump and Heat Recovery Systems Communicate

Quick Answer

My thermostat won't let me select Heat. Why?

If it's a Fujitsu heat pump (2-pipe) system, every indoor unit must be in the same mode, either heating or cooling. When one unit is in Cool, the controllers won't offer Heat. This is normal, not a fault. Turn the entire system off, including all indoor units, and wait 3 minutes. All modes will then reappear on every controller.

The Golden Rule: Last Call Wins

On any VRF system, the last controller to send a command wins. Whichever thermostat most recently selects a mode, the system follows. How far that mode reaches depends on the type of system.

Heat Pump Systems: One Mode for Everyone

A heat pump system can't heat and cool at the same time, so all indoor units must share one mode. Once someone selects a mode, every other thermostat on the system has to follow it. Central controllers are no exception, and they also won't show Heat while the system is in cooling.

When a contractor says their thermostat only offers Cool and Dry, first verify the system type. On a heat pump system, that behavior is by design.

Out of the box, the fix is to turn the whole system off, every indoor unit, and wait 3 minutes. After that, all mode options reappear on whichever controller you're using.

Better Control: Set a Master Indoor Unit

My favorite fix for Fujitsu heat pump systems is to give mode control to a single thermostat:

1. At the outdoor unit, go to the F2 menu and set function code 21 to 02. This allows a master indoor unit to select the mode.
2. Pick the thermostat that best represents the building, the one that's the best guide for whether it needs heating or cooling.
3. At that indoor unit, set it as the master indoor unit.

Now only that thermostat controls the mode. You can leave it in Auto so it switches between heating and cooling on its own, or make it the one spot where a tenant can change modes.

Setpoints stay independent at every zone. Even in cooling mode, a zone that has reached setpoint won't overcool.

Heat Recovery Systems: Mode Control Per Port

Heat recovery systems (3-pipe, with branch boxes) provide simultaneous heating and cooling, so the system-wide mode lock doesn't apply. Each branch box port, and the units it feeds, is independently mode-selectable. One room can heat while another cools.

There's one catch. If multiple indoor units share a single port, everything downstream of that port behaves like a heat pump system. Those units must share a mode, and last call wins. If rooms or tenants need true independent control, give each its own port.

Which System Should You Choose?

For apartments, or offices with separate rooms, heat recovery is usually the better fit. Heat pump systems can work, but they offer less control and tend to generate tenant complaints when occupants want different modes.

Troubleshooting Checklist: "My Thermostat Won't Let Me Select Heat"

1. Identify the system type: heat pump (2-pipe) or heat recovery (3-pipe with branch boxes).
2. Heat pump: Another unit is likely in Cool, so Heat isn't offered. This is normal.
3. Reset the mode: Turn off the entire system, including all indoor units. Wait 3 minutes. All modes reappear.
4. Remember last call wins: The last controller to select a mode sets it for the system.
5. Set up a master indoor unit (heat pump only): In the outdoor unit's F2 menu, set function code 21 to 02. Then set your chosen indoor unit as the master indoor unit. Only that thermostat will control the mode.
6. Heat recovery: Check whether the units share a branch box port. If so, apply steps 2 to 4 to those units.
7. Setpoints are independent: A zone at setpoint won't overcool, even in cooling mode.