Bosch No Heat / Burner Not Firing

Furnace runs but does not produce heat; the blower or pump operates but the burner never ignites.

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.

Possible Causes

Thermostat not calling for heat or miswired, gas supply shut off, faulty gas valve, ignition control lockout not reset.

Safety: If you smell gas, do not attempt to light the furnace. Evacuate and call your gas supplier.

Thermostat: Confirm the room thermostat or Bosch controller is set to HEAT and above the current room temperature. Replace batteries if applicable.
Gas valve: Ensure the manual gas shutoff valve near the furnace is parallel to the pipe (open). Check that other gas appliances are working.
Reset lockout: Many Bosch furnaces have a reset button on the control or burner. Press and hold as specified in the manual to clear the lockout. If the unit repeatedly locks out, stop resetting it and investigate further.

Gas valve and ignition control testing should be performed by a licensed technician.

Medium 3/5

Gas Valve Assembly

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