Kidde FENWAL 35-71 Series Manual Download Page 2

Page: 2 / 8

Start up - Heat Mode

120 VAC is supplied to the L1 terminal, either from a thermostat or other control
device. When this occurs the control will power up and perform a self-check
routine and if selected, begin a pre-purge. Following the pre-purge, the gas valve
is energized and sparks commence until flame is detected or the Trial for Ignition
(TFI) period expires.

When flame is detected, the spark is shut off and the gas valve and combustion blow-
er remain energized. The thermostat, pressure switch and main burner
flame are constantly monitored to ensure that the system is functioning properly.
When the thermostat is satisfied and the demand for heat ends, the gas valve
is de-energized immediately and a post-purge is initiated (optional) and the
flame is extinguished. When the post purge is complete, the combustion blower
is de-energized.

System Response to Flame Failures

Fenwal controls are configured with several options for managing loss of flame.

Failure during TFI Period

SINGLE TRIAL MODEL

Should the burner fail to light or flame is not detected during the
TFI period, the gas valve is de-energized and the control will go into
lockout mode.

MULTI TRIAL MODEL

Should the burner fail to light or flame is not detected during the
first TFI period, the gas valve is de-energized and the control will
attempt two additional ignition trials with inter-purge. If these
attempts are unsuccessful, the control will go into lockout mode.

Failure of Established Flame - Two Options

There are two methods for re-starting the burner after loss of established flame.
The Re-ignition option is the default configuration for re-establishing flame and
does not need to be specified when ordering. If the Recycle option is desired,
please specify this when ordering so that a special part number is assigned to
the control by Fenwal.

RE-IGNITION

If the established flame signal is lost, the control responds and begins
sparking within 0.8 seconds of loss of flame. This is considered the first
re-ignition attempt. The spark will be energized for the duration of the
TFI period in an attempt to re-light the burner. If flame is re-established,
normal operation resumes.

SINGLE TRIAL MODEL

If the burner does not light after the first re-ignition attempt, the
control will de-energize the gas valve and go into lockout mode.

MULTI TRIAL MODEL

If the burner does not light after the first re-ignition attempt, the inter-
purge sequence is completed between the next two attempts to re-light
the burner. If the burner fails to light after the third attempt, the control
will de-energize the gas valve and go into lockout mode.

RECYCLE

If the established flame signal is lost, the control responds
by shutting off the gas valve within 0.8 seconds.

SINGLE TRIAL MODEL

The control will begin the ignition cycle with the pre-purge cycle,
if a pre-purge cycle is programmed into the control. Controls without
pre-purge immediately commence sparking for one TFI period. If flame
is re-established, normal operation resumes. If the burner fails to light
after the first try, the control will de-energize the gas valve and go into
lockout mode.

MULTI TRIAL MODEL

The control will begin the ignition cycle with the inter-purge sequence
and attempt three tries for ignition including inter-purges. If flame is
re-established, normal operation resumes. If the burner fails to light
after the third try, the control will de-energize the gas valve and
go into lockout mode.

NOTE:

The Recycle feature option requires a special part number that

is determined by contacting Fenwal.

Combustion Air Flow Monitoring

In normal operation, the control monitors the combustion air flow by reading
the pressure switch (PSW) input to confirm that the blower is operating in the
proper sequence. Initially, the control checks the PSW input to be sure that
it is open. Once the blower is energized and the PSW closes the control
proceeds to trial for ignition.

If during a call for heat 120 VAC power is present at the PSW input prior to
the blower being energized, the control will wait 30 seconds, for the condition
to change. Possible reasons for this condition includes a stuck or mis-wired
pressure switch, or the blower is spinning down and keeping the switch closed.
If the condition does not change, an airflow fault will be declared and the LED
will flash the one flash pattern.

If the combustion blower is energized and the PSW does not close within
30 seconds, an airflow fault will be declared and the LED will flash the one-
flash pattern. The blower will remain energized until the condition changes.

If the PSW signal is lost while the burner is firing, the control will immediately
de-energize the gas valve and the combustion blower will remain on. If the
call for heat remains and the PSW signal returns within 30 seconds, the control
will restart with the pre-purge period. If the PSW input does not return within
30 seconds, the blower remains on and LED will flash the one-flash code
indefinitely. If the PSW closes, the LED stops flashing and the control resumes oper-
ation with the pre-purge function.

Lockout Mode (On-Board Safety System)

After single or multiple attempts to light the burner have failed or flame is not estab-
lished, the control automatically enters lockout mode. The control will not open the
gas valve unless there is intervention by the user or one hour has
passed depending on the model chosen. See Lockout Recovery.

Lockout Recovery - Two Options

There are two options for recovering from lockout mode. When selecting
the control, please specify one of the following methods for lockout recovery.

1. Thermostat/ Power Off Reset- requires the user to reset the thermostat below

ambient temperature or remove the 120 VAC power supply for 5 seconds.
The control will start the ignition sequence and attempt to light the burner again.

2. Automatic Reset - After one hour, if the thermostat is still calling for heat, the

control will automatically start the ignition sequence and attempt to light the
burner again.

Benefits of Full Time Power

1. Separate 120 VAC input for ignition control operation and combustion blower

operation. Allows high current to feed the blower directly rather than have it
pass through the thermostat.

2. Sense flame even with zero second pre-purge to provide safe operation.

Control will monitor flame presence immediately upon a call for ignition.

3. Post purge blower operation to clear the combustion chamber and remove

remaining heat when the call for heat has ended.

4. If a flame is detected during pre-, inter- or post-purge, the combustion

blower will be energized. Should the main valve later close and the flame
signal disappear, the combustion blower will be de-energized.

Page 2