OPERA
TION & CONTROLS
27
Control Logic - Flow Chart
YES
YES
Blower “Pre-Purge”
for 45 sec
Spark
Unit Heating until
demand is satisfied.
Is Water Setpoint,
Temperature and
“Heating” displayed?
Was Water
Temperature
reached?
Blower “Post-Purge”
for 3 minutes
Wait for new Heat
demand
END
NO
NO
Diff Sw Closed
Diff Sw Open
Fan Lockout
Ing Try Failure
Ign 60 min Delay
Ignition Lockout
Check for damaged or loose wires and terminals.
Check Gas valve, Gas supply and spark igniter:
- Check gas supply and valve operation.
- Check Igniter and wire. Replace if damaged.
Check Blower and Air Pressure switch:
- Replace Pressure switch if failing open or close.
- Replace Blower if operation is intermittent.
Clock/Fireman Sw
Water Sw Open
Vent Sw Open
Hi Limit 1 Fault
Hi Limit 2 Fault
Cabinet Temp Lm
Switch connected to safety loop is in OFF mode.
Air SW Open
Diff Sw Fault
Fan Lockout
Flame Lost
Flame Flickering
Flue Over Temp
Low Flow Fault
High Flow Fault
Verify water flow / pressure. Clean Filter/Strainer.
Vent switch open. Troubleshoot extractor if installed.
Temperature Limit switch open. Verify water flow.
Inspect internal thermostat (Unitherm Governor) and
bypass valve.
Air Pressure Switch failed in operation. Verify Blower
operation. Check for air inlet/outlet obstructions. Verify
air pressure.
Verify gas supply. Verify gas valve operation.
Cut power, verify and clean igniter rods.
Verify obstructions. Troubleshoot extractor if installed.
Verify water flow. Verify Pump operation. Adjust Flow
as necessary. Verify filter pressure and clean if needed.
Check for damaged or loose wires and terminals.
Outlet Over Temp Verify water flow. Verify gas supply and combustion.