Janitrol GMP125-5 REV A L Furnace Manual

The Janitrol GMP125-5 REV A L is a high-efficiency gas furnace with 125,000 BTU input capacity, single-stage operation, natural gas compatibility, multi-speed blower motor, electronic ignition system, aluminized steel heat exchanger, and safety features including flame rollout switch, pressure switch, and limit controls. Designed for residential forced-air heating systems with AFUE rating up to 80%. Below are key sections for safety, features, installation, operation, maintenance, and troubleshooting.

1. Features at a Glance 2. Installation Requirements 3. First-Time Startup 4. Technical Specifications 5. Controls and Settings 6. Venting and Combustion Air 7. Operation Procedures 9. Maintenance Schedule 10. Regulatory Compliance 11. Troubleshooting Guide

Features at a Glance

Key components: Aluminized steel heat exchanger, hot surface igniter, induced draft blower, multi-speed PSC blower motor, gas valve, flame sensor, control board.

FeatureDescription
Heat ExchangerAluminized steel tubular design for durability
Ignition SystemHot surface electronic ignition
Blower MotorMulti-speed PSC motor for airflow control
Gas ValveSingle-stage natural gas operation
Control BoardIntegrated furnace controller with LED status lights
Safety DevicesFlame rollout switch, pressure switch, high limit switch
VentingCategory I venting required
Electrical120V AC, 60Hz power supply
Thermostat ConnectionStandard 24V thermostat terminals
Filter SizeStandard 16x25x1 inch filter

Installation Requirements

Professional installation required. Verify local codes and obtain permits.

  1. Location: Install in approved locations with proper clearances to combustibles.
  2. Venting: Use approved Category I vent materials; maintain proper slope.
  3. Gas Supply: Connect with black iron pipe; pressure test for leaks.
  4. Electrical: Connect to dedicated 120V circuit; proper grounding required.
  5. Ductwork: Size appropriately for 125,000 BTU output; seal all connections.

WARNING! Gas furnaces produce carbon monoxide; improper installation can be fatal. Only qualified technicians should install.

First-Time Startup

Complete installation verification before initial startup.

  1. Gas pressure check: Verify manifold pressure at 3.5" WC for natural gas.
  2. Venting verification: Confirm proper draft and combustion air supply.
  3. Electrical check: Verify 120V supply and thermostat wiring.
  4. Sequence test: Initiate heating cycle; observe ignition sequence.
  5. Temperature rise: Measure 35-65°F temperature rise across heat exchanger.
  6. Combustion analysis: Verify CO levels below 100 ppm in flue gases.

CAUTION! Never bypass safety devices. Test all safety controls before operation.

Technical Specifications

Controls and Settings

Integrated control board with status LED. Access door switch for service access.

Control Board LED Codes: Steady green = normal operation; 1 flash = pressure switch error; 2 flashes = ignition failure; 3 flashes = rollout switch trip; 4 flashes = high limit trip.

Blower Speeds: Heating speed typically tap #3; cooling speed typically tap #4. Gas Valve: Single-stage operation with manual shutoff. Thermostat: Standard 24V connections (R, W, G, Y, C).

Venting and Combustion Air

Category I venting required. Follow NFPA 54 and local codes.

  1. Vent Material: Use B-vent or approved listed venting materials.
  2. Vent Termination: Minimum 12" above ground level; clear of windows/doors.
  3. Combustion Air: Provide adequate combustion and dilution air per code requirements.
  4. Vent Length: Maximum equivalent vent length per installation instructions.

Tip: Install carbon monoxide detectors in sleeping areas when using gas appliances.

Operation Procedures

Normal heating cycle operation sequence.

  1. Call for heat: Thermostat closes R-W circuit.
  2. Inducer start: Induced draft blower energizes for pre-purge.
  3. Pressure switch: Proves draft established.
  4. Ignition: Hot surface igniter glows for 17-30 seconds.
  5. Gas valve: Opens to main burner.
  6. Flame sense: Flame sensor confirms ignition.
  7. Blower start: Blower motor energizes after heat exchanger warm-up delay.
  8. Cycle completion: Thermostat satisfied, gas valve closes, blower continues for post-purge.

WARNING! Never operate without access doors properly installed. Keep combustible materials away from furnace.

Maintenance Schedule

Annual professional maintenance recommended. Monthly filter changes during heating season.

FrequencyMaintenance Task
MonthlyCheck/replace air filter
AnnuallyProfessional inspection and cleaning
AnnuallyCheck heat exchanger for cracks
AnnuallyClean burners and flame sensor
AnnuallyCheck gas pressure and combustion
AnnuallyInspect vent system and clearances
AnnuallyLubricate blower motor if required
AnnuallyCheck safety controls operation

Regulatory Compliance

ANSI Z21.47/CSA 2.3: Certified for US and Canada. UL listed. Follows NFPA 54 National Fuel Gas Code. Installation must comply with local building codes. For technical support, contact Janitrol at 1-800-654-3286 or visit www.janitrol.com.

Troubleshooting Guide

SymptomPossible CauseCorrective Action
No heatThermostat, power, gas supplyCheck thermostat setting; verify power; check gas valve position.
Furnace won't startDoor switch, fuse, limit switchEnsure access doors closed; check fuse/circuit breaker; reset limit switch.
Blower runs continuouslyThermostat fan settingSet thermostat fan to AUTO mode; check fan limit control.
Ignition failureGas pressure, igniter, flame sensorCheck gas supply; inspect igniter for damage; clean flame sensor.
Short cyclingDirty filter, restricted airflowReplace air filter; check for blocked vents/registers.
Unusual odorsDust buildup, overheatingClean burners and heat exchanger; check for proper airflow.
Loud noisesBlower wheel, inducer motorInspect for debris; check motor bearings; tighten components.

Reset Procedure: Turn off power for 30 seconds, then restore.

Service: 1-800-654-3286; www.janitrol.com

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