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VZ-VZH-VZT-IOM (08-24) 1047121-A
OPERATION—CONTINUED
Startup
1. Close manual shutoff valve to turn OFF gas.
2. Turn OFF electric power.
3. Wait 5 minutes for unburned gases to vent from heater.
4. Ensure that combination gas valve is open and open manual shutoff to turn ON gas.
5. Turn ON electric power.
6. Set thermostat to desired temperature—burner should light automatically.
Sequence of Operation
Table 16. Sequence of Operation
Action Result
Turn up thermostat
Thermostat calls for heat
Blower motor energizes
As blower motor approaches nominal
running RPM, pressure switch closes
Ignition control module activates
Ignition control module opens
combination gas valve after 45-second
pre-purge period
Spark igniter energizes
Flame is established
Sparking sequence ceases
For model VZT, burner operates on low- or high-fire depending on demand sensed by
thermostat—during low-fire operation, low-fire burner status indicator light is illuminated—during
high-fire operation, both low- and high-fire burner status indicator lights are illuminated
If flame is not established during ignition
sequence . . .
Ignition control module closes combination gas valve and purge period begins
Ignition control module will try two additional ignition attempts with purge periods in between trials
If ignition is not established, ignition control module locks out*
If flame extinguishes during operation . . .
Ignition control module closes combination gas valve and purge period begins
Ignition control module will try two additional ignition attempts with purge periods in between trials
If ignition is not re-established, ignition control module locks out for 1 hour or until reset*
When thermostat is satisfied . . . All power to unit is shut OFF
*After lockout, the ignition control module can be reset by turning down the thermostat for 5 seconds and then raising it again to the desired
temperature or by disconnecting and then reconnecting power to the unit.
Post-Startup Checklist
Check the following after startup:
With unit in operation, measure manifold (outlet) gas pressure in accordance with Measure and Adjust Manifold
Gas (Outlet) Pressure section.
Check operation of flame safeguard: with heater running normally, shut off gas supply—heater should attempt
to re-light and then lock out.
Turn unit OFF and ON—pausing 2 minutes between each cycle—observe for smooth ignition.
Place literature bag that contains Limited Warranty, this manual, and any control or optional information in
accessible location near heater.
Shutdown
1. Set thermostat to lowest setting.
2. Turn OFF electric power.
3. Turn OFF manual shutoff gas valve.
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