Lennox International Inc MPB35ST-NM Troubleshooting, Symptom Possible Causes Corrective Action

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TROUBLESHOOTING

Note: Before troubleshooting the gas control system, Ensure external gas shut off valve, located at gas supply inlet, (and wall switch, iff applicable), is

in the “ON” position. Important: Valve system troubleshooting should only be accomplished by a qualified service technician.

TROUBLESHOOTING GUIDE - MILLIVOLT GAS CONTROL SYSTEM

 

SYMPTOM

POSSIBLE CAUSES

CORRECTIVE ACTION

1.

Spark igniter will not light pilot after

A. Defective igniter

Check for spark at electrode and pilot; if no spark and

 

repeated triggering of igniter button.

(no spark at electrode).

electrode wire is properly connected, replace igniter.

 

 

B. Defective or misaligned electrode at pilot

Using a match, light pilot. If pilot lights, turn off pilot

 

 

(spark at electrode).

and trigger the igniter button again. If pilot lights, an

 

 

 

improper gas mixture caused the bad lighting and

 

 

 

a longer purge period is recommended. If pilot will

 

 

 

not light – check gap at electrode and pilot – should

 

 

 

be 1/8" to have a strong spark. If gap measures 1/8",

 

 

 

replace pilot (see Figure 17 on Page 14).

 

 

C. Gas supply pressure errant.

Check inlet gas pressure. It should be within the limits

 

 

 

as marked on the rating plate.

 

 

D. Pilot orifice plugged.

Clean or replace pilot orifice.

2.

Pilot will not stay lit after

A. Defective pilot generator

Check pilot flame, it must impinge on thermocouple

 

carefully following the lighting

(thermocouple).

(see Figure 17 on Page 14). Clean and/or adjust pilot

 

instructions.

 

for maximum flame impingement on thermocouple.

 

 

 

Ensure that the connection between the valve and

 

 

 

thermocouple are tight and secure.

3.

Pilot burning, no gas to burner, Valve

A. Manual Reset Spill Switch has Tripped or is

Follow Manual Reset procedure on Page 6. Once the

 

knob “ON,” and the (standard) burner

defective.

red reset button is fully depressed and clicks in, check

 

OFF/ON switch is “ON." Read impor-

 

continuity with a multimeter between switch terminal

 

tant note below.

 

 

 

(Ohms). If it shows an open circuit, replace switch.

 

 

 

 

 

 

 

 

IMPORTANT NOTE: If an optional

B. Wall switch or wires defective.

Check wall switch and wires for proper connections.

 

 

Jumper wire across terminals at wall switch, if burner

 

*remote switch is used for burner

 

comes on, replace defective wall switch. If okay, jumper

 

operation, the standard burner

 

wires across wall switch wires at valve, if burner comes

 

OFF/ON switch on appliance must

 

on, wires are faulty or connections are bad.

 

be in the "OFF" position.

 

 

 

C. Thermopile may not be generating suf-

Check thermopile with millivolt meter. Take reading

 

 

 

*Optional remote switch kits - wall

ficient millivolts.

at thermopile terminals of gas valve. Should read

 

switch or remote control.

 

325 millivolts minimum with optional wall switch

 

 

 

“OFF.” Replace faulty thermopile if reading is below

 

 

 

specified minimum.

 

 

D. Plugged burner orifice.

Check burner orifice for blockage and remove.

 

 

 

 

 

 

E. OFF/ON Switch & *Remote Switch are in

When turning on the burner using a *remote switch,

 

 

the "ON" position resulting in excessive

ensure that the standard OFF/ON switch is in the "OFF"

 

 

resistance.

position. If both switches are in the ON position, it

 

 

 

may result in excessive resistance (& millivolt drain-

 

 

 

age) and the burner may not come on.

4.

Frequent pilot/burner outage prob-

A. Pilot flame may be too low or blowing (high)

Clean and/or adjust pilot flame for maximum flame

 

lem.

causing the pilot/valve safety to drop out.

impingement on thermocouple (see Figure 19 on

 

 

 

Page 20).

TROUBLESHOOTING GUIDE - ELECTRONIC IGNITION SYSTEM

 

SYMPTOM

 

POSSIBLE CAUSES

CORRECTIVE ACTION

 

 

 

 

1.

Burner will not light.

A. Faulty Valve System.

See Below.

 

 

 

 

 

 

B. “OFF/ON” or wall switch defective.

Disconnect the two black wires from the wire nuts.

 

 

 

 

Test switch(s) for continuity with a multimeter. If

 

 

 

 

continuity is not indicated, switch(s) is defective and

 

 

 

 

must be replaced.

 

 

 

 

Note: Before replacing “OFF/ON” switch, Ensure to

 

 

 

 

check wiring for loose connections or broken wires

 

 

 

 

and repair as needed.

 

 

 

 

2.

Burners come “ON,” then turns “OFF.”

A. Burner orifice plugged.

Check main burner orifice(s) for blockage. Clean

 

 

 

 

or replace.

 

 

 

 

 

 

B. Obstructed vent system.

Check vent system for obstructions.

 

 

 

NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.

 

 

 

 

 

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Contents 875,024M REV. NC 04/2005 MPB35ST-NMMPB35ST-NE MPB35ST-PMListing Agency OTL Report No -F-27-5 Congratulations Safety & Warniing Information Burn-in PeriodOrifice Sizes Sea Level to High Altitude All Models Burner Orifice Sizes all models Elevation Natural PropaneOperation and Care of Your Appliance Millivolt AppliancesSIT Millivolt Valve see FigureSpill Switch Operation Vent Operation TestEnsure Appliance is OFF Pilot only and Cool Maintenance Outside Combustion Air ControlsGlass Front See Figure Top View of Logs Top View of Logs Installed CA BLOG SET ReferencePlacement of Glowing Embers Read LOG Warnings on page 9 Before ProceedingRemove front glass enclosure panel from appliance Position The Groove in The Back of Log CBurner Adjustments Qualified Technicians only Air Shutter Adjustment GuidelinesThis appliance is not designed to burn wood. Any attempt to Flame Appearance & SootingMaintenance Task Accomplishing Person Procedure While HOTTroubleshooting Symptom Possible Causes Corrective ActionSwitch or remote control Operation, the standard burnerTroubleshooting Procedure Electronic Ignition System Warranty Replacement PartsWiring Diagrams Lennox Hearth ProductsAccessory Components Clean Face Panel Kits Brickaded Panel Liner KitScreen Heat Guard Kit Door Frame KitsArch Door Kits Polished Brass and Brushed Stainless Hood KitsPiece Polished Brass and Brushed Stainless Louvers Kits Outside Air Kits Models FOAK-4 and FOAK-4LDNormal service To OFF. Do not force Lighting InstructionsTo Turn OFF GAS to Appliance What to do if YOU Smell GASSwitch What to do if YOU Smell GASClose lower control compartment door To Shut OFFReplacement Parts MPB35ST 20 P/N 875,024M REV. NC 04/2005West Taft Avenue Orange, CA

MPB35ST-NM specifications

Lennox International Inc., a leader in the heating, ventilation, and air conditioning (HVAC) industry, offers the MPB35ST-NM model as part of its comprehensive range of integrated solutions. This finely engineered unit is designed to provide exceptional performance and energy efficiency while ensuring optimum home comfort.

One of the standout features of the Lennox MPB35ST-NM is its modular design, which allows for flexible installation and easy integration with existing systems. This unit is particularly beneficial for residential settings where space may be at a premium. It also supports efficient zoning, enabling tailored climate control for different areas of the home.

The MPB35ST-NM utilizes advanced multi-stage heating technology, which means it can adjust its output to match the specific demands of the environment. This significantly enhances energy efficiency and reduces operational costs. The unit operates with a high Seasonal Energy Efficiency Ratio (SEER) rating, ensuring optimal performance without excessive energy consumption.

Additionally, the MPB35ST-NM is equipped with smart technology features that allow homeowners to monitor and manage their heating system remotely. Through a user-friendly app, users can adjust settings, schedule maintenance reminders, and receive performance alerts, all of which contribute to an improved user experience.

Another key characteristic of the MPB35ST-NM is its quiet operation. The unit is designed with sound-dampening components that minimize noise during operation, ensuring that homeowners can enjoy a peaceful living environment.

Durability is another hallmark of Lennox products, and the MPB35ST-NM is no exception. Constructed with high-quality materials, this unit is built to withstand the rigors of daily use while offering long-lasting reliability. Additionally, Lennox provides robust customer support and warranty options, giving customers peace of mind in their investment.

In summary, the Lennox International Inc. MPB35ST-NM model stands out as a leader in home heating solutions. With its adaptable design, energy-efficient technology, smart features, quiet operation, and dependable durability, it meets the evolving needs of modern households, making it an excellent choice for those seeking comfort and efficiency in their heating systems.
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