Flame Sensors for a Ruud Furnace Achiever 90 Plus Manual

The Ruud Furnace Achiever 90 Plus is a high-efficiency gas furnace with advanced flame sensor technology that ensures safe and reliable operation. The flame sensor detects the presence of a flame during ignition and continuously monitors it during operation to prevent gas leaks and ensure proper combustion. Below are key sections covering safety, features, installation, maintenance, troubleshooting, and replacement procedures for the flame sensor system.

Flame Sensor Overview

The flame sensor is a critical safety component that detects flame presence using a rod that generates microamp current when heated by the burner flame. This signal confirms proper ignition and allows the gas valve to remain open.

Safety Precautions

Always follow safety protocols when working with furnace components.

1. Turn off electrical power at circuit breaker before servicing.
2. Shut off gas supply valve before any maintenance.
3. Allow furnace to cool completely before accessing components.
4. Use proper tools and personal protective equipment.
5. Verify proper operation after any service work.

WARNING! Failure to follow safety procedures may result in fire, explosion, or carbon monoxide poisoning. Only qualified technicians should perform flame sensor maintenance.

Installation Guidelines

Proper installation ensures reliable flame detection and furnace operation.

1. Position sensor rod directly in flame path of main burner.
2. Ensure proper clearance from burner tubes (1/4 inch recommended).
3. Secure mounting bracket firmly to prevent vibration.
4. Route sensor cable away from hot surfaces and moving parts.
5. Connect to designated flame sensor terminals on control board.

CAUTION! Incorrect sensor positioning may cause false flame detection or failure to detect flame.

Technical Specifications

• Sensor Type: Flame rectification rod
• Material: 304 Stainless Steel
• Operating Temperature: Up to 1500°F
• Signal Output: 1-10 microamps DC when flame present
• Resistance: Less than 1 ohm when clean
• Length: 3.5 inches standard
• Thread Size: 1/4 inch NPT mounting
• Wiring: 18 AWG high-temperature rated

Operation and Monitoring

The flame sensor works in conjunction with the ignition control system during each heating cycle.

Normal Operation Sequence: Gas valve opens > igniter heats > spark ignition > flame sensor detects flame > control board confirms flame > system continues operation.

If flame is not detected within 4-7 seconds, control board closes gas valve and enters lockout mode after 3 attempts.

Maintenance Procedures

Regular maintenance prevents flame sensor failure and ensures reliable operation.

1. Annual inspection recommended for normal use.
2. Bi-annual inspection in high-dust environments.
3. Check for proper microamp reading (3-8 μA typical).
4. Inspect for physical damage or corrosion.
5. Verify secure electrical connections.

Tip: Schedule maintenance before heating season for optimal performance.

Cleaning the Flame Sensor

Cleaning removes carbon buildup that can interfere with flame detection.

1. Turn off power and gas supply to furnace.
2. Remove sensor mounting screw and carefully pull sensor out.
3. Clean rod with fine steel wool or emery cloth.
4. Wipe with lint-free cloth to remove debris.
5. Reinstall sensor and restore power/gas.
6. Test furnace operation.

WARNING! Do not use abrasive materials that may scratch sensor surface. Avoid touching cleaned surface with bare hands.

Replacement Instructions

Replace flame sensor if cleaning doesn't restore proper operation or if physical damage is present.

1. Obtain Ruud OEM replacement part (Part #: 62-24077-01).
2. Disconnect power and gas supply.
3. Remove old sensor and mounting hardware.
4. Install new sensor in same position and orientation.
5. Secure mounting bracket and reconnect wiring.
6. Restore utilities and test operation.

CAUTION! Use only manufacturer-approved replacement parts to maintain safety and warranty coverage.

Troubleshooting Common Issues

Regulatory Compliance

Flame sensor meets UL 795 and ANSI Z21.47 standards for commercial and industrial gas-fired appliances. Certified for use with natural gas and propane systems. Complies with NFPA 54 National Fuel Gas Code requirements for flame safeguard systems.

Error Codes and Diagnostics

The Ruud Achiever 90 Plus control board displays error codes related to flame sensor issues:

• Code 13: Limit circuit lockout - Check flame sensor reading
• Code 21: Gas valve circuit error - Verify flame detection
• Code 33: Limit control open - May indicate flame rollout
• Code 44: Flame sensed with gas valve off - Replace flame sensor

Service: Contact Ruud certified technician at 1-800-722-2704 or visit www.ruud.com