1. External Limit Tripped
2. Insufficient flow for Flow Switch
3. Tripped Thermal Fuse
4. Tripped High Vent Pressure Switch
1. Indication that an external limit (wired to “LIM”) is open. Not a problem with boiler, check external limit.
2. Check plumbing, ensure circulator is operating.
3. Check Thermal Fuse on the back of the heat exchanger (accessed from the rear of the cabinet). If tripped contact NTI.
4. The high vent pressure switch will trip when the combustion chamber is blocked or venting is too restrictive. Check venting and clean combustion chamber.
