Sequence Of Operation Flow Chart - A.O. Smith BTH-120 Instruction Manual

seQuence of operation flow chart

If tank temperature drops below Operating Set Point minus
Differential setting a heating cycle is activated
Normal State of all pressure switches and ECO are checked
All other pressure switches and ECO are verified closed
Water is heated to
set point
24 Volt Gas Valve
de-energized
30 second
Post-Purge cycle
Water heater goes
into standby mode
Control System performs diagnostic checks
Blower Prover pressure switch verified open
Combustion Blower is energized
Pre-Purge cycle
Blower Prover switch contacts confirmed
closed by control system
Igniter is energized for warm up period
Does Control System sense minimum
Igniter amps?
24 Volt Gas Valve is energized
gas flows to Main Burner
Is flame sensed at the Main Burner ?
(control system monitors the flame sensor)
YES
NO
NO
NO
NO
24 Volt Gas Valve
de-energized
30 second
Inter-Purge cycle
Retries up to
two more times
Control System
Locks Out
"Ignition Failure"
Fault Msg is
displayed
figure 62
59
Control System Locks Out
Displays Fault Msg
Control System Locks Out
"Blower Prover Open"
Fault Msg is displayed
Control System Locks Out
"Low Igniter Current"
Fault Msg is displayed
2.0 minimum AC amps