Navien CH-180, Service Manual, Page: 102 / 155

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Error occurrence conditions and check items
5.22. 28Error
Error Description
1. Space heating water pressure of 7.3 psi or lower is maintained for over 5
minutes, the system displays 28E (regardless of initial power supply).
2. If the space heating water pressure of 7.3 psi or lower is detected, and becomes
7.3 psi or lower in 2 hours after water refilling, the system displays 28E. (The
error is not displayed until 72 hours is passed after the power is connected
initially.)
1. Check the water pressure sensor.
2. Check if the boiler is installed in a low water pressure area.
28E
Leakage
Check
items
Does the water leak
out of pipe?
No
Yes
No
*AWS: Auto Water Supplement
Check*AWS valve
or connector
Voltage between pin1 and pin3 of CN21 is 120VAC
After press the reset button,
Does water supplement
occurred?
Check into pipe and
pipe assembly
No
Yes
No
Replace main PCB
Yes
Does water supplement
terminated within 5min?
Normal state Yes
During AWS valve operation,
is the output voltage of AWS
valve normal?
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