Tempstar 40VA Transformer 115V to 24V for T8DNL125L20B2 — OEM 1172810 | Ships Today

Overview

This genuine OEM control transformer (part number 1172810) steps the incoming 115-volt line down to the 24-volt control voltage that powers the Tempstar T8DNL125L20B2 furnace's thermostat circuit, gas valve, integrated control board, and relays. Rated at 40VA, it delivers the low-voltage power the entire control system relies on. A failed control transformer is a frequent no-heat cause: when it opens or shorts internally, the thermostat goes dark, the control board loses its 24V supply, and the furnace will not respond to a heat call. Watch for a blank thermostat, no furnace response, a burnt smell near the control box, or a low-voltage fuse that blows repeatedly.

Specifications

Compatibility

Designed for the Tempstar T8DNL125L20B2 furnace and other ICP-family (Tempstar, Heil, Comfortmaker) gas furnaces using a 115V-to-24V 40VA control transformer. Verify primary/secondary voltages and VA rating against your existing transformer before installing.

Installation Guide

1. Safety First — Disconnect power at the furnace disconnect and verify zero voltage with a multimeter.
2. Access — Remove the furnace service panel to expose the control box and transformer.
3. Document — Photograph all primary and secondary leads before disconnecting.
4. Remove — Label and disconnect the wires, then unbolt the failed transformer from its bracket.
5. Install — Mount the new transformer and reconnect the 115V primary and 24V secondary leads per your photo.
6. Test — Restore power, confirm 24V across the secondary, and verify the thermostat and furnace respond to a heat call.

Signs You Need a Replacement

• Blank or unpowered thermostat
• Furnace will not respond to a heat call
• Burnt smell or scorching near the control box
• Repeatedly blown 3A low-voltage fuse

Shipping & Returns

Ships same day before 3 PM CST. 30-day returns. National HVAC Parts fitment guarantee.