Thermo Pride Gas/Propane Furnace Induced Draft Highboy/Counterflow/Horizontal MHA1 - Manual (Page 46)

All installations and services must be performed by qualified service personnel.
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APPENDIX B: SEQUENCE OF OPERATIONS
A. Sequence of Operations for Heating System
Control System Action
Ignition control module
energized,draft inducer starts.
After ignitor warm-up, the
automatic gas control valve
is energized to open.
Mode of Operation
Standby
(At any time the gas
valve is not energized)
Start
Start trial for
ignition
Continous safe operation check. If
flame simulation condition present
or roll-out switch opens,system
energizes inducer fan and circulator
blower at high speed until situation
correction occurs.
Thermostat calls for heat,
contacts close
Pressure switch senses
adequate pressure,
contacts close.
On power interruption, system
shuts off, restarts when
power is restored.
If flame is not detected, the
gas valve is de-energized,
the ignitor is turned off and
the ignition control module
goes into the "Retry" sequence.
Power is applied to the hot
surface ignitor. Ignitor warms-
up for 20 seconds.
Flame must be detected
within 4 seconds. If flame
detected, the delay-to-fan-
on time begins (45 seconds)
The retry sequence
provides a 60 second
wait before ignition retry.