Service Manual

For models with Honeywell Integrated Control

System w/ Direct Spark Ignition

Thermostat calls for heat.

Combustion blower & circulator start while the damper opens.

Blower pre-purge period of 30 seconds.

Trial for Ignition. (5 seconds, 3 trials).

Flame establishing period (3 seconds), gas valve opens, sparks from spark rod to burner surface to ignite

the gas.

Burner on, flame proving period (2 seconds). Requires a minimum of 0.8 microamp through flame sense

rod to prove flame.

If either blocked vent safety switch contacts (normally closed) or circulator flow switch and damper contacts

(normally open) remain open after being energized, then the ignition sequence will not start and an error

code 29 (Safety switch circuit failed to close

or open) will be shown on the display.

Steady State Operation: Burner continues to operate until:

Thermostat circuit opens, gas valve closes, blower continues to operate for 30 second post-purge period.

If the normally closed blocked vent safety switch opens, the gas valve closes, the blower post-purges, then

shuts off with error code 26 displayed in a lockout condition.

Thermostat satisfied.

Gas valve closes, burner extinguished.

Blower post purge for

30 seconds.