TROUBLESHOOTING PROCEDURE - ELECTRONIC IGNITION SYSTEM

START

CHECK

• Turn Off Gas Supply.

 

• Check for proper volt-

 

 

 

• Ensure Valve Switch Is In ON Position.

 

age at control harness

 

•

Line voltage power

• Disconnect Control Harness.

 

(see insert A). Voltage

NO

•

Low voltage transformer

• Set Thermostat To Call For Heat.

2

should be 24V between

 

•

Limit controller

 

thermostat or pressure

 

• Thermostat

 

 

 

 

 

 

•

Wiring

 

 

switch and 24V common

 

 

 

 

 

 

 

 

and 24V hot.

 

 

 

 

 

YES

 

 

 

Insert A

• Plug control harness into

 

valve. Wait for internal check

End View of Control Harness Connector

delay.

 

 

 

24 Volt Hot

24 Volt

 

 

 

 

 

• With pilot burner cable con-

 

 

Common

 

 

 

 

1

 

 

 

 

 

 

NO

 

nected, measure voltage at

NO

 

 

 

 

• Igniter warms up and glows

 

 

• Replace valve.

 

 

 

 

 

 

valve HSI element output. 24V

 

 

 

 

 

red.

 

 

 

 

 

 

 

 

 

 

 

 

2

 

 

 

 

 

 

 

 

 

nominal. (See insert B)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

YES

 

 

24 Volt

 

 

1

YES

 

• Replace igniter/flame rod

 

 

 

 

 

 

 

 

assembly.

 

 

Switched

 

 

 

 

 

 

 

 

Check For Damaged or Missing

 

 

 

 

 

 

YES

 

 

 

 

 

 

 

 

 

 

 

Terminals in Connector

 

 

 

NO

• Check that pilot gas is flowing. Wait

NO

 

 

 

 

• Turn on gas supply.

 

to ensure pilot gas tubing is purged.

• Replace valve.

 

 

 

 

 

 

 

 

• Pilot burner lights.

 

 

Recycle call for heat if necessary.

 

 

Insert B

 

 

 

 

 

 

 

 

YES

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Igniter Terminals

 

 

 

 

• Measure voltage between 24V hot and

 

 

 

 

 

 

 

 

24V common leads to valve control.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Must measure at least 19.5 VAC with

NO

• Check transformer and

 

 

 

 

 

 

 

 

igniter powered (see insert A). To

line volt supply.

 

 

 

 

 

YES

 

 

identify proper lead, this check must

 

 

 

 

 

 

 

 

 

be done with the valve control con-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

nected and igniter powered.

 

 

 

 

 

 

 

 

 

 

 

YES

 

 

 

 

 

 

 

 

 

•

Replace Pilot Assembly.

 

 

 

 

 

 

 

 

 

•

Check that pilot flame makes good

 

 

 

 

 

 

 

 

 

 

contact with pilot burner flame rod.

 

 

 

 

 

•

Main valve opens and main

NO

• Check for good electrical connection

 

 

 

 

 

 

burner lights.

 

 

through the pilot tubing.

 

 

 

 

 

 

 

 

 

• If both of the above are good, replace

 

 

 

 

 

 

 

 

 

 

igniter/flame rod assembly.

 

 

 

 

 

 

 

YES

 

 

 

YES

 

 

 

 

 

• System Is okay.

 

• Cycle thermostat off and back on.

 

 

1

Igniter

will cycle off

and

2

When measuring voltage

 

 

 

 

 

 

back on once during the 90

at connections, use care

 

 

 

 

NO

 

 

 

 

 

 

 

 

 

second

ignition trial.

All

 

to ensure terminals are

 

•

Main burner lights.

 

• Replace valve.

 

voltage measurements must

 

not damaged.

 

 

 

 

 

 

 

be taken while the igniter is

 

 

 

 

 

 

 

 

 

powered.

 

 

 

 

 

 

 

 

 

NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.

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Lennox Hearth MPD35ST-PM, MPD35ST-NM, MPD35ST-NE manual Troubleshooting Procedure Electronic Ignition System
Page 18 Page 20

MPD35ST-NE, MPD35ST-PM, MPD35ST-NM specifications

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One of the standout features of the MPD35ST series is its innovative Direct Vent technology. This system draws air from the outside for combustion, eliminating the need for indoor air and thereby reducing energy consumption and improving indoor air quality. This feature not only enhances efficiency but also provides a safe and comfortable environment for your home.

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