Cause of error code 3

Boiler Safety Limit  Open

Boiler Safety Limit, or External Limit wired to terminals J5-1 OPEN:
-Jumper for External Limit wired to terminals 11 and 12 or device connected        to it open.
-Flow Switch contact open.

Solution for error code 3

See possible causes for “Hard Lockout 4”.
Loose wiring to limit device.
External Limit defective or jumper not installed.
If yellow light on LWCO is on, system is low on water.
If neither yellow or green light is on, check LWCO harness.
Flow Switch contact open - Check for adequate flow.
Bad Flow Switch.