Operating Sequence; Operating Sequence When Wired As Shown - Smith HW 420 Instruction Manual

All units are built with an ignition control module that provides the
ignition sequence, pilot flame monitoring, and safety shut off of
the gas valves. The CSD-1 ignition control modules are of two
15 seconds pilot trials with 5 minutes waiting period between the
two trials. If the pilot flame is not established/confirmed during
the first 15 seconds ignition trial, or if the pilot flame signal is lost
after main burner is ON, the United Technologies (UT) ignition
module will de-energize the gas valve and wait for 5 minutes. It
will start one more 15 seconds trial for ignition. If the pilot flame
is still not established, the alarm contacts on the ignition module
will be energized, which will cause the CSD-1 lockout module to
shut down the power to the ignition module and illuminate the red
LED. The ignition module will be in "Lockout" mode until the reset
button on the lockout module is pressed.

OPERATING SEQUENCE WHEN WIRED AS SHOWN

1. With power supplied the unit becomes activated.
2. When the System Controller (i.e., tank temperature control,
thermostat, building controller, etc.) closes "calling for heat",
power will activate the circulating pump. Power is also
supplied to the normally open contacts of the flow switch.
3. With the pump providing sufficient water flow, the flow switch
will close contacts; allowing power to be supplied to the
transformer through the manual reset high limit.
4. Power continues through the normally closed auto reset
high limits to energize the ignition control module. Opening
the contacts on either high limit immediately shuts down the
control module.
5. Once energized, the control module tries for ignition by
starting a control timer, opening the pilot gas valve (PV) and
generating a high voltage pulse. Gas and ignition sparks are
supplied at the pilot until the pilot lights or the control timer
terminates the ignition trial.
If the pilot does not light, or the module does not recognize
a stable flame, the module will de-energize the gas valve for
5 minutes, then starts the second and last 15 second trial for
ignition.
6. When the pilot flame has been established and accepted
by the control module sensing circuit, power is allowed to
energize the main gas valve (MV). This valve opens, allowing
gas to flow to the main burner which is then ignited by the pilot
flame. Failure of the pilot flame at any time during operation
will cause the control module to shut down the gas valve.
7. The system continues to operate until "call for heat" is
satisfied. The unit then shuts down. The thermal balancer
keeps the pump operating approximately one (1) extra
minute for heat exchanger post-purge. The unit will continue
to operate automatically as required.

OPERATING SEQUENCE

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