H1 code during heating mode, outdoor unit runs but little heat output

Note: On some Fraser‑Johnston heat pumps, H1 indicates the unit is in defrost mode and is not a fault if temporary.

• Observe duration: If H1 appears only briefly and then heating resumes, this is normal defrost operation.
• Check outdoor coil: If H1 stays on and heating is poor, inspect the outdoor coil for heavy frost or ice. Clean the coil and ensure the outdoor fan is operating.
• Verify sensors: Check the outdoor coil thermistor and ambient sensor for proper attachment and resistance values.
• Control board: If defrost cycles are excessively long or frequent, the defrost control on the outdoor PCB may be malfunctioning and require replacement.