Boiler displays F5 and may cycle frequently without heating properly

Safety first: Turn off power before working on low-voltage wiring.

Steps:

• Locate outdoor sensor: Find the Peerless outdoor reset sensor on the north or northwest exterior wall.
• Inspect cable: Check for cuts, staples through the wire, or UV damage.
• Test sensor: Disconnect at the boiler control and measure resistance. Compare to Peerless outdoor sensor chart. Replace if out of range.
• Bypass temporarily: Some controls allow disabling outdoor reset in the menu to restore basic operation until the sensor is replaced.