A.O. Smith 750 SERIES, GB/GW-300, 500, 650 warranty See below

“Blocked Flue” Flue is Blocked Continuous SOFT

•Caused by the blocked flue switch contacts being open when they should have been closed. Check for flue blockage, switch contacts, wiring.

“High Limit” Outlet temp. exceeded high limit setpoint Continuous Auto Reset

•Caused when the temperature of the outlet probe exceeds the high limit setpoint. This is an internal “software” limit switch and not an actual device. Check that the over temperature is not being caused by improper setup or operation of the boiler.

“ECO fault” Outlet temp is too high Flashing HARD

•Caused when the ECO contacts in the Outlet probe are open when they should be closed. Fault may be due to high outlet temperature, bad switch contacts in the ECO, or disconnected wiring. Note: The ECO can be checked by disconnecting the outlet probe from the CCB and reading the resistance across the two active pins on the connector at the end of the probe cable. The value should be approximately 0 ohms when the temperature of the probe is less than 220°F.

“Low Water” Water level is too low Flashing HARD

•Caused by the Low Water Cut Out device not closing its feedback switch contacts when it should. Check water line, switch contacts, wiring LWCO.

“Low Gas” Gas pressure is too low Flashing HARD

•Caused by the Low Gas switch being open when it should be closed. Check gas line, switch contacts, wiring.

“IRI Gas” IRI Gas Valve did not turn on Flashing HARD

•Caused by the IRI Gas Valve not closing its feedback switch contacts when it should. Could also be caused by a problem with the relay output on the CCB. Check output to IRI Gas Valve, switch contacts, wiring.

“Powered Vent” Power vent not running Flashing HARD

•Caused by the Powered Vent device not closing its feedback switch contacts when it should. Could also be caused by a problem with the relay output on the CCB. Check output to powered vent, switch contacts, wiring.

“High Gas Stg*” Gas pressure too high Flashing HARD

•Caused by the High Gas switch being open when it should be closed. Check gas line, switch contacts, wiring.

“Inlet Probe” Inlet probe shorted or open Flashing HARD

•Caused when the thermistor in the probe or the wiring to the probe is shorted or disconnected. Check the probe. Note: The thermistor and wiring can be checked by disconnecting the probe from the CCB and reading the resistance across the two active pins on the connector at the end of the probe cable. The value should be approximately 10K ohms (value will change slightly with changes in temperature).

“Outlet Probe:” Outlet probe shorted or open Flashing HARD

•Caused when the thermistor in the probe or the wiring is shorted or disconnected. Check the probe. Note: the thermistor and wiring can be checked by disconnecting the probe from the CCB and reading the resistance across the two active pins on the connector at the end of the probe cable. The value should be approximately 10K ohms (value will change slightly with changes in temperature).

“Tank Probe” Tank (Remote) probe shorted or open Flashing HARD

•Caused when the thermistor in the probe or the wiring is shorted or disconnected. Check the probe. Note: the thermistor and wiring can be checked by disconnecting the probe from the CCB and reading the resistance across the two active pins on the connector at the end of the probe cable. The value should be approximately 10K ohms (value will change slightly with changes in temperature).

“Igniter Stg*” Igniter current is too low Flashing HARD

•Caused by a low current draw problem with the Silicon Carbide Igniter. This may occur if the igniter is old, damaged, or disconnected and no longer draws the proper level of current. This condition will affect the ability of the igniter to get hot enough to fire the gas properly. Check the igniter and its associated wiring.

“Igniter Pwr Stg*” Improper power applied to Silicon Carbide circuit Flashing HARD

•Caused by improper line power being applied to the Silicon Carbide circuit. Check line connections. Paying particular attention to the earth ground connection. Also check that line voltage does not exceed 132 vac rms.

“Igniter Hdwr Stg*”	Hardware problems with Silicon Carbide circuit	Flashing	HARD
"Gas Relay Stg*"	Gas Valve Relays did not turn on	Flashing	HARD
"Flame Stg*"	Flame not detected	Flashing	HARD
"Blwr Low Stg*"	Low speed blower relay did not turn on	Flashing	HARD
•	Caused by a failure of a relay on the FCB. Contact factory.
"Blwr Hi Stg*"	High speed blower relay did not turn on	Flashing	HARD
•	Caused by a failure of a relay on the FCB. Contact factory.
"Short Cycle Cond."	Burner cycle rate above 30 per hour	SEE BELOW	- - - -

•Caused when a stage performs more than 30 heat cycles in one hour. When this fault is detected the system continues to operate but the calls for heat are forced to occur no faster than every 180 seconds. While this system is in this short cycle operating mode the yellow "Standby" LED flashes. Check system setup and operation.