Fenwal 35-665721-101 Control

The Fenwal 35-665721-101 is a microprocessor-based 24V Hot Surface Ignition (HSI) control designed for precise burner sequencing in gas-fired equipment. This MiniIgnition control features a 4-second Trial for Ignition (TFI) and a 15-second pre-purge cycle to exhaust residual gases from the combustion chamber, ensuring a safe start-up. Built with a single-trial ignition logic (1TRY), the 35-665721-101 provides reliable flame monitoring and utilizes Detect-A-Flame technology for rapid response to flame failure, typically within 0.8 seconds. This module is an essential HVAC ignition module replacement for systems requiring integrated blower relay control and microprocessor-governed timing for consistent performance in demanding environments.

Key Benefits:

• Enhanced Safety: The 15-second pre-purge clears the heat exchanger before the hot surface ignitor is energized, reducing the risk of delayed ignition.
• Precise Ignition Timing: Microprocessor circuitry ensures accurate 4-second TFI, providing a consistent window for the gas valve and ignitor synchronization.
• Integrated Blower Control: Features an on-board inducer blower relay, streamlining wiring for 24VAC HSI systems.
• Diagnostics: Includes system LED indicators for rapid troubleshooting of airflow faults, ignition lockout, and internal circuit health.
• Durability: Conformal-coated PCB provides moisture resistance in non-condensing environments, maintaining signal integrity at operating temperatures up to 176°F.

Common Questions:

How do I troubleshoot an ignition lockout on the 35-665721-101?
Technicians should observe the diagnostic LED. Three flashes typically indicate a lockout. Verify 24 VAC at the R terminal, check for a cracked silicon carbide ignitor, and ensure the flame sensor is producing at least 1.0 microamp DC of flame current.

Does this control require a full-time 24V power supply?
Yes, this model is designed for systems where the R terminal provides constant power to the microprocessor, allowing the Fenwal 35-665721-101 to maintain volatile memory and diagnostic status during the appliance cycle.

What is the maximum current rating for the gas valve terminal?
The gas valve output is rated for up to 2.0A at 24 VAC, making it compatible with most standard residential and commercial gas valves used in hot surface ignition applications.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.