Tempstar 40VA Transformer for T8MPV125J20A1 — 115V to 24V | Ships Today

Overview

This is a genuine OEM control transformer (part number 1012722) for the Tempstar T8MPV125J20A1 gas furnace. It steps 115V line voltage down to the 24V control voltage that powers the thermostat, gas valve, igniter circuit, and control board. Rated at 40VA, it supplies the full low-voltage demand of the furnace. When this transformer fails, the entire 24V control system goes dead — the thermostat may go blank and the furnace will not respond to a heat call even with 115V present at the primary. Audible buzzing, an open internal thermal fuse, or the smell of scorched insulation indicate the transformer should be replaced.

Specifications

Compatibility

Built for the Tempstar T8MPV125J20A1 furnace and shared across the ICP family (Heil, Comfortmaker, Arcoaire, KeepRite) using the same 40VA 115V-to-24V control transformer. 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 the primary and secondary leads.
2. Access — Remove the furnace control/blower compartment service panel.
3. Document — Photograph all primary and secondary wiring before disconnecting.
4. Remove — Label and disconnect the primary and secondary leads, then unbolt the failed transformer from its mounting bracket.
5. Install — Mount the new transformer, reconnect leads exactly per your photo, and secure all connections.
6. Test — Restore power and verify 24V across the secondary and normal furnace operation on a call for heat.

Signs You Need a Replacement

• No 24V output while 115V is present on the primary
• Dead thermostat or furnace that ignores the heat call
• Buzzing, humming, or burnt smell from the transformer
• Control fuse on the board repeatedly blows

Shipping & Returns

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