Bosch
No Heat Call from Thermostat
Thermostat powers on but does not call for heat even when room is cold and setpoint is higher than room temperature.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Incorrect system type configuration (set to cooling only), Heat call (W) wire not connected or broken, Heat disabled in installer settings, Faulty heat relay output on thermostat
How to Fix / Troubleshooting
Safety: Turn off power to the HVAC system before changing wiring.
- Check mode and setpoint: Ensure the thermostat is in HEAT or AUTO mode and the setpoint is above room temperature.
- Verify wiring: Confirm the W (or W1) wire is connected at both the thermostat and the Bosch boiler/furnace control board.
- Installer settings: In the advanced menu, verify that heating is enabled and that the correct system type (heat pump vs. conventional) is selected.
- Bypass test: At the control board, with power on, temporarily jumper R to W. If the boiler/furnace starts, the issue is likely with the thermostat or its wiring.
- Replace thermostat if needed: If wiring is intact and equipment responds to a jumper but not to the thermostat, the thermostat’s heat output may be defective.
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Repair Difficulty
Medium
3/5
Required Part
Bosch Smart Thermostat Main Control Assembly
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