Navien NCB300-28K, Service Manual

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Troubleshooting 83
5.3.2 Water Temperature Issue
Error type Cause Check method
Boiler is not operating
properly.
Front panel power off Hot water does not run if the front panel is switched off.
Defective flow sensor
The boiler does not work due to the defective flow sensor.
●
The flow sensor impeller will not rotate if it contains excessive scale or
debris. Clean out the flow sensor if possible.
●
If the impeller rotates normally, replace the flow sensor back into the boiler.
●
The sensor may be reused temporarily after cleaning, but replacement is
recommended.
Defective hot water
temperature sensor
The temperature is sensed higher than the actual temperature due to a
defective hot water (cold water) sensor.
●
Hot water temperature is low although hot water is recognised by the
boiler.
●
The cold water temperature sensor may not be working properly.
Low hot water
temperature
Hot water setting error Check the hot water temperature setting on the front panel.
Water mixed with cold
water.
The temperature of hot water at the tap is low while the temperature is high
at the hot water outlet.
●
Cold water and hot water are mixed due to improper pipe installation.
●
Cold water and hot water are mixed due to improper piping at the hot
water faucet.
No hot water from the
valve
Check the pipe
1. The cold water valve is closed.
2. Check if the cold water filter is clogged with foreign substance.
3. Check if the cold water / hot water pipes are frozen during the winter.
4. The main heat exchanger is clogged (by scale).
5. Low inlet water pressure
Cold water flows
temporally
Pre-heating does not
work
The system initiates the internal / external circulation preheating when a
recirculation mode is selected on the front panel DIP switches. Confirm the
DIP switch settings.