Weil McLain 591-391-818 Wiring Harness

The Weil McLain 591-391-818 Control Module to Circulator Wiring Harness is the factory harness that connects a boiler's control module to its circulator. Weil McLain's GV Series 1 and 2 parts list includes 591-391-818, so it is a manufacturer-listed part for those gas boilers and not a generic extension lead. The harness is terminated with a connector, and the product photo shows it laid out next to rulers for scale.

When a circulator harness is damaged, the symptoms are often intermittent. A circulator that does not start on a call for heat, a pump that runs when it should not, or a control module that appears healthy while the circulator never responds can all trace back to a cracked insulation jacket, a heat-damaged plug or a corroded terminal. Replacing the whole harness with the 591-391-818 restores the original connection between the control module and the circulator and avoids splicing wire in a spot where heat and vibration are constant.

Before you order, compare the connector on the old harness with the product photo and confirm the boiler is a GV Series 1 or 2. Other Weil McLain harnesses carry different part numbers and are not interchangeable, so the part number on the old harness or the boiler model and serial number is the quickest way to be sure.

Key Benefits

• Listed for GV Series 1 and 2: 591-391-818 appears in the Weil McLain GV Series 1 and 2 parts list, so it is a manufacturer-specified harness for those boilers.
• Complete Harness Replacement: Replaces the whole run from the control module to the circulator instead of a splice repair in a hot, vibrating location.
• Connector Terminated: Arrives with its connector in place, so the module and circulator connections plug back in the way they were built.
• Clear Part Number Match: One manufacturer number, 591-391-818, to match against the old harness or the parts list.

Common Questions

• What does the 591-391-818 connect? It is the control module to circulator wiring harness for Weil McLain gas boilers listed in the GV Series 1 and 2 parts list.
• Does it fit every Weil McLain GV boiler? No. Other GV series use different harness numbers. The 591-391-818 is shown in the GV Series 1 and 2 parts list, and our team can confirm fit if you send the boiler model and serial number.
• Can I repair the old harness instead? A damaged jacket or burned plug is better handled by replacing the harness. Splices and field-made repairs sit in a hot area and tend to fail again.

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.