F16 error; heater will not start and may blow internal fuse repeatedly.

Safety first: Turn off power at the breaker. Only work on internal electrical components if you are comfortable and qualified.

• Check internal fuse: Remove the control panel and locate the low-voltage fuse on the control board. If blown, replace only with the same type and rating.
• Inspect low-voltage wiring: Look for pinched or shorted thermostat, sensor, or communication wires that could be blowing the fuse.
• Test transformer (advanced): With power on and extreme caution, measure the transformer’s secondary voltage to ensure it matches specifications. If no output, the transformer is likely bad.
• Persistent fuse blowing: If the new fuse blows immediately, disconnect external low-voltage connections and try again. If it still blows, the control board or transformer may be shorted and require professional replacement.