John Wood Commercial - 300-400K BTU - Manual (Page 55)

55
seQuence of operation flow chart
YES NO
Water is heated to
set point
24 Volt Gas Valve
de-energized
30 second
Inter-Purge cycle
24 Volt Gas Valve
de-energized
Retries up to
two more times
30 second
Post-Purge cycle
Control System
Locks Out
“Ignition Failure”
Fault Msg is
displayed
Water heater goes
into standby mode
If tank temperature drops below Operating Set Point minus
Differential setting a heating cycle is activated
Blower Prover switch contacts confirmed
closed by control system
Igniter is energized for warm up period
24 Volt Gas Valve is energized
gas flows to Main Burner
Is flame sensed at the Main Burner?
(control system monitors the flame sensor)
Control System Locks Out
Displays Fault Msg
NO
Control System Locks Out
“Blower Prover Open”
Fault Msg is displayed
NO
Control System Locks Out
“Low Igniter Current”
Fault Msg is displayed
NO
Combustion Blower is energized
Pre-Purge cycle
Does Control System sense minimum
Igniter amps?
Control System performs diagnostic checks
Normal State of all pressure switches and ECO are checked
Blower Prover pressure switch verified open
All other pressure switches and ECO are verified closed
2.0 minimum AC amps
300,000 N & P and
400,000 P Btu/hr models
3.1 minimum AC amps
400,000 N Btu/hr models
figure 58