Water Temperature Issue - Navien NCB-700-2S+/42K Service Manual

5.3.2 Water Temperature Issue

Error type
Boiler is not operating
properly.
Low hot water
temperature
No hot water from the
valve
Cold water flows
temporally
Cause
Front panel power off Hot water does not run if the front panel is switched off.
The boiler does not work due to the defective flow sensor.
●
Defective flow sensor
●
●
The temperature is sensed higher than the actual temperature due to a
defective hot water (cold water) sensor.
Defective hot water
●
temperature sensor
●
Hot water setting error Check the hot water temperature setting on the front panel.
The temperature of hot water at the tap is low while the temperature is high
at the hot water outlet.
Water mixed with cold
●
water.
●
1. The cold water valve is closed.
2. Check if the cold water filter is clogged with foreign substance.
Check the pipe 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
The system initiates the internal / external circulation preheating when a
Pre-heating does not
recirculation mode is selected on the front panel DIP switches. Confirm the
work
DIP switch settings.
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.
Hot water temperature is low although hot water is recognised by the
boiler.
The cold water temperature sensor may not be working properly.
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.
Check method
Troubleshooting 103