Fenwal 35-665725-121 Ignition Control

The Fenwal 35-665725-121 Ignition Control is a microprocessor-based Direct Spark Ignition (DSI) module designed for the precise management of gas-fired heating systems. This 24VAC ignition control provides a robust three-try ignition sequence, incorporating a 15-second pre-purge, 30-second inter-purge, and 30-second post-purge to ensure safe combustion cycles. Engineered for high-demand environments, it features a built-in combustion blower relay and is compatible with 24VAC mini-ignitors requiring a 4-second heat-up time. The module is conformal coated to withstand up to 95% relative humidity, making it a reliable choice for furnaces, boilers, and commercial gas appliances. With a Trial for Ignition (TFI) of 4 seconds and a flame sensitivity threshold of 0.7 microamps, this control ensures stable flame monitoring and system safety across a wide temperature range of -40°F to +176°F.

Key Benefits for Contractors

• Multi-Try Ignition Strategy: Increases system reliability by attempting three trials before lockout, reducing nuisance service calls in natural, LP, or manufactured gas applications.
• Integrated Blower Control: Simplifies wiring with an onboard combustion blower relay rated up to 3.0 FLA at 120 VAC.
• Durable Construction: The Gray Noryl N-190 enclosure provides superior physical protection, while the conformal coating prevents moisture-related circuit failure.
• Standardized Diagnostics: Microprocessor monitoring allows for consistent sequence of operation, including critical pre-purge and post-purge cycles for venting safety.

Common Questions

What is the difference between this and a single-try module?
The 35-665725-121 provides three ignition attempts before entering a hard lockout, whereas single-try models lock out immediately if the flame is not sensed during the first TFI, making this model more resilient to environmental variables.

Can I use this with a standard 120V Hot Surface Ignitor (HSI)?
No, this specific control is engineered for 24 VAC mini-ignitors. Always verify the voltage of your ignitor element to prevent component failure.

How does the flame sensing work?
This module utilizes a flame rectification circuit. It requires a minimum signal of 0.7 microamps to maintain the gas valve relay; ensure your burner ground and electrode placement are optimal for consistent signal strength.

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.