Use and Care Manual

6-580.15

START-UP PROCEDURE

Control Operating Sequence

All units are supplied with intermittent pilot systems with

continuous retry control as standard. For intermittent pilot

systems, both the main burner and pilot are turned off 100%

when the thermostat is satisfied. For all units, the system

will attempt to light the pilot for 70 seconds. If the pilot is not

sensed, the ignition control will wait approximately 6 minutes

with the combination gas control closed and no spark. After

6 minutes, the cycle will begin again. After 3 cycles, some

ignition controllers lockout for approximately 1 hour before the

cycle begins again. This will continue indefinitely until the pilot

flame is sensed or power is interrupted to the system. Refer to

Table 18.1 for control code descriptions. Specific descriptions of

the control sequence for different control codes are listed below.

1. The thermostat calls for heat.

2. The power exhauster relay is energized, starting the power

exhauster motor. Once the motor has reached full speed, the

differential pressure switch closes.

3. The pilot valve opens and the ignitor sparks for 70 seconds

in an attempt to light the pilot.

4. Once the pilot is lit, the flame sensor proves the pilot and

stops the ignitor from sparking.

5. On single stage units, the main gas valve is opened and the

main burner is lit to 100% full fire. On two stage units, the

gas valve may open at either 50% or 100%, depending on

what the two stage thermostat is calling for.

6. The air mover starts after 30 to 90 seconds to allow the heat

exchanger to warm up.

7. The unit continues to operate until the thermostat is satisfied,

at which time both the main and pilot valves close 100%.

8. The air mover stops after 30 to 90 seconds to remove

residual heat from the heat exchanger.