Navien NCB300-28K, Service Manual

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56 Troubleshooting
5.2.1 Error 001
Error Conditions and Checklist
Error Description
E001
Heat exchanger overheat
1. If the space heating water temperature is higher than 105°C, E001 will be displayed on
the front panel to warn users of high temperature conditions.
2. If the space heating water temperature decreases below 105°C, E001 will
automatically reset and the boiler will repeat the combustion cycle.
3. If the overheat error is repeated consecutively three times, E001 will be displayed until
the boiler is manually reset.
Checklist
1. Check the operation of the circulation pump. Run it in test mode.
2. Check the operation of the 3-way valves. Run it in test mode.
3. Check if the heating strainer is obstructed.
4. Check if the main heat exchanger or the DHW heat exchanger is obstructed.
5. Check the heating inlet / outlet valve and distribution piping for obstructions.
6. Check the PCB DIP switch settings.
7. Check the PCB is operating properly.
8. If the fault condition remains after these checks, replace the PCB.
Scenario
Verify the thermistor readings
at the front panel. Are the DHW
thermistor readings normal?
Verify the items in the checklist
Before measuring the thermistor’s resistance,
disconnect it from the PCB.
Measure the thermistor resistance.
(Refer to the thermistor resistance table.)
Replace the supply thermistor
Yes
No