The Fenwal 35-655908-003 is a microprocessor-based hot surface ignition control designed for gas-fired heating equipment that requires reliable ignition sequencing and flame supervision. This control supports 24 VAC appliance operation and is commonly used in HVAC, furnace, boiler, water heater, and similar gas-burner applications.

This ignition control manages the heating demand sequence by energizing the hot surface ignitor, opening the gas valve, monitoring flame establishment, and supporting safe burner operation. The Series 35-65 and 35-66 controls are designed to monitor heat demand, control ignition operation, maintain flame during the heating cycle, and provide diagnostic support through onboard LED output.

The 35-655908-003 has a 24 VAC hot surface ignition control with 0-second prepurge and a 7-second trial for ignition, making it suitable for compatible systems where this ignition timing is required.
 

Frequently Asked Questions

• What is the Fenwal 35-655908-003 used for?

The Fenwal 35-655908-003 is a 24 VAC hot surface ignition control used in compatible gas-fired heating equipment. It helps manage ignition sequencing, flame monitoring, and burner operation.
 

• What type of ignition control is this?

This is a hot surface ignition control, also called an HSI control module. It is part of Fenwal’s 35-65 / 35-66 microprocessor-based ignition control series.
 

• What voltage does the Fenwal 35-655908-003 use?

The control operates on 24 VAC.
 

• What is the trial for ignition timing?

This model has a 7-second trial for ignition, commonly written as 7 sec TFI.
 

• Does this ignition control have prepurge timing?

Yes. The 35-655908-003 is listed with 0-second prepurge timing.
 

• What fuel types is this control used with?

Available product data lists this control for natural gas, propane, and manufactured gas applications.
 

• Does the control include diagnostic support?

Yes. The Fenwal 35-65 / 35-66 series includes onboard LED diagnostics to assist with troubleshooting ignition and burner operation.
 

• What is the operating temperature range?

The listed temperature range is -40°F to 176°F.
 

• Is the Fenwal 35-655908-003 a universal replacement?

No. It should be matched to the appliance’s required voltage, ignition timing, wiring configuration, flame sensing method, and approved replacement part list before installation.
 

• Who should install this ignition control?

Installation should be performed by a qualified HVAC technician or service professional because the module controls gas ignition and flame safety functions.