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10. FLUE GAS TEMPERATURE PROBE SHORT/OPEN
The ue gas temperature is mounted near the exhaust connection to monitor the ue gas temperature leaving the water heater.
Flue gas temperature probe short, fault code 0x4B, indicates that the probe’s resistance measured between the two connectors of the
probe is below 394 ohms. If the probe’s resistance is conrmed low using an ohm meter, replace the probe.
Flue gas temperature probe open, fault code 0x4C, indicates that the probe’s resistance measured between the two connectors of the
probe is above 32500 ohms. If the probe’s resistance is conrmed above 32500 ohm using a ohm meter, replace the probe, otherwise
check the wiring connections.
Figure 14. Flue Gas Temperature Probe
11. FLUE GAS TEMPERATURE HIGH LIMIT
The ue gas temperature is mounted near the exhaust connection to monitor the water heater’s exhaust temperature. If the heater is
running during the makeup mode with inlet water temperature around 70°F, the exhaust temperature is normally around 100°F leaving
the water heater. If the heater is running during the standby mode, the ue exhaust temperature tends moving up during the standby
heating cycle. The water heater will turn off if ue temperature reaches 170°Fand reset at 160°Ffor heater to restart. If the ue
temperature reaches 175°F, ue gas temperature high limit fault ( fault code 0x51) will display on UIM and heater will be turned off,
check the pump and the secondary HEX for potential blockage, and use 10K thermistor chart to check the probe’s performance.
12. FLOW NOT DETECTED
A water ow switch is installed at the outlet of the secondary HEX to conrm water owing through the secondary HEX whenever the
heater is running. During the standby, the pump is off and ow switch opens. During the heating cycle, the recirculation pump is
energized as soon as the main burner ame is sensed, the ow switch closes by the owing water inside the piping. At the end of the
heating cycle, the pump is de-energized with 5 seconds delay after the gas valve is turned off, ow switch opens back.
Pump
Flow
Check
Valve
Flow
Switch
Figure 15. Flow Detection Components
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