Navien CH-180, Service Manual, Page: 92 / 155

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Error occurrence conditions and check items
5.17. 18Error
Error Description
If an error (open: 14 ı or lower) in the space heating return thermistor is detected
continuously for 3 seconds, the system displays the 18E error message. The boiler
maintains the Safety-Shutdown status, and if the heating temperature is sensed
normally, stops postpurge, and returns to the standby mode.
1. Check if the thermistor is open and if the connector is connected properly.
2. Check if the thermistor is defective.
3. Defective PCB.
18E
Space
heating
return
thermistor
open
Check
items
Is the Return thermistor
normal?
Yes
No Replace Return thermistor
Resistance between two black wires of CN 13 is from 0.8 to 20 KO
at normal condition.
Check connector
Caution : Before measuring resistance of the thermistor,
remove the connector form the PCB.
© Navien Ameri c a I n c . 20 1 0 CH series servi c e Manua l Version 1 .0