Limit Circuit Open (Safety)
Control has sensed a fault in the safety limit circuit; check the following:
1. External Limit (Purple wire) – if an external limit device (i.e. LWCO) is connected to the purple wire at the field wiring terminal, check to ensure it has not tripped, and that it is wired correctly.
2. Internal Limit (Heat Exchanger Thermal Fuse) – the heat exchanger is equipped with a normally closed thermal fuse; the fuse opens when the heat exchanger gets too hot. If the fuse is open, contact NTI
