50
Control Logic – Flow Chart
YES
YES
YES
YES
Blower “Post-Purge”
for 3 minutes
Wait for new Heat
demand
END
START
NO
NO
NO
• Check On/Off switch (under lid on control panel)
• Check for 240 or 120 volts to the transformer
(time clock, circuit breaker, wire connections)
• Check for 24 volts to Circuit Board (P6 connector)
Is a Fault Message displayed?
NO
“Remote” and Water Temperature displayed?
If Remote mode is set to control the heater,
Exit Remote control by pressing UP + DOWN.
YES
Inlet , Outlet or Vent
Temp [Open/Short]
Gas Valve
Flame w/o CFH
Low Voltage
Verify sensor per “Temperature-Resistance” table:
- Replace Sensor if readings are out of range.
- Replace Ignition board if sensor readings are right.
Check voltage at valve terminals. If terminals are
energized replace control boards, if not replace valve.
Check main voltage if voltage is below 23VAC.
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.
In Sensor Fault
Check for damaged or loose wires and terminals.
Inlet , Outlet or
Flue Sensor
[Open/Short]
Fahrenheit (°F)
Temperature-Resistance
Celsius (°C)
Inlet Sensor (kΩ)
Outlet Sensor (kΩ)
Flue Sensor (kΩ)
6.3
-14
open
short
40
4
261
26
1.03
50
10
199
20
1.09
60
15
153
15
1.14
70
21
119
12
1.19
80
27
93
9.3
1.25
90
32
73
7.3
1.35
100
38
58
5.8
1.57
110
43
46
4.6
1.77
187
86
short
short
open
Fahrenheit (°F)
Celsius (°C)
< 7.5
< -13
50
10
75
24
100
38
125
51
150
65
200
93
300
149
400
204
464
240
open
Below Above
Temperature-Resistance
Below Above
MODEMODE
UPUP
DOWNDOWN
Power On
Is the Display lit?
Push MODE
Select “Pool” or “Spa”
Push UP or DOWN
arrows to adjust
Temperature
Is Water Setpoint and
Water Temperature
displayed?
Blower “Pre-Purge”
for 45 sec
Spark
Is Water Setpoint,
Temperature and
“Heating” displayed?
Unit Heating until
demand is satisfied.
Was Water
Temperature
reached?
Control Logic - Flow Chart
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