Thermo Products Thermo Pride Furnace MHA1-75N User's Manual | Page 46

Thermo Products Furnace User's Manual - Thermo Pride Furnace MHA1-75N.
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All installations and services must be performed by qualified service personnel. 
 

43 

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. 

 

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