Boiler shows E07, no heat, circulator may run without burner firing

Safety: Turn off power before working on control wiring.

Steps:

• 1. Locate outdoor sensor: Find the small sensor mounted on an exterior north or northwest wall, away from direct sun. Inspect for physical damage.
• 2. Check wiring: Follow the low-voltage cable from the sensor back to the boiler control. Look for cuts, staples through the wire, or loose connections at the control terminals.
• 3. Tighten connections: With power off, remove and reinsert the sensor wires at the control terminals, ensuring a solid connection.
• 4. Temporary bypass (for testing only): A technician may temporarily install a resistor of the correct value or a known-good sensor to verify control operation. Do not leave the system with an improper sensor permanently.

When to call a pro: If wiring is intact and E07 persists, the outdoor sensor or the control board input is likely defective and should be tested and replaced by a qualified technician.