Tempstar 40VA Transformer for T8MPV125J20C1 — 115V to 24V | Ships Today

Overview

This is a genuine OEM control transformer (part number 1172810) for the Tempstar T8MPV125J20C1 gas furnace. It steps line voltage of 115V down to the 24V low-voltage control circuit that powers the thermostat, gas valve, igniter, and control board. Rated at 40VA, it supplies enough capacity to drive the furnace's full complement of 24V loads. When a transformer fails, the entire low-voltage control system goes dead: the thermostat screen may go blank, the furnace will not respond to a call for heat, and you will read 115V on the primary but little or no 24V on the secondary. A buzzing transformer, a tripped internal thermal fuse, or scorched windings are all signs the unit needs replacement.

Specifications

Compatibility

Engineered for the Tempstar T8MPV125J20C1 furnace and shared across the ICP family of brands (Heil, Comfortmaker, Arcoaire, KeepRite) that use the same 40VA 115V-to-24V control platform. Always confirm the part number stamped on your existing transformer before ordering.

Installation Guide

1. Safety First — Disconnect power at the furnace switch and breaker, then verify zero voltage with a multimeter on both primary and secondary leads.
2. Access — Remove the furnace control/blower compartment service panel.
3. Document — Photograph all primary and secondary wire connections before disconnecting anything.
4. Remove — Label and disconnect the line-voltage primary leads and the 24V secondary leads, then unbolt the failed transformer from its mounting bracket.
5. Install — Mount the new transformer, reconnect primary and secondary leads exactly per your photo, and secure all wire nuts.
6. Test — Restore power and confirm 24V across the secondary terminals and normal furnace operation on a call for heat.

Signs You Need a Replacement

• No 24V output on the secondary while 115V is present on the primary
• Thermostat is dead or furnace ignores the heat call
• Buzzing, humming, or burnt smell from the transformer
• Repeated control-fuse blowing on the board

Shipping & Returns

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