Tempstar 40VA Transformer for T8MPT100J20B1 - 115V to 24V | Ships Today

Overview

This OEM 40VA control transformer (Tempstar part 1172810) steps line voltage down from 115V to the 24V low-voltage power that runs the furnace control board, thermostat, gas valve, and relays in the Tempstar T8MPT100J20B1. Every call for heat depends on clean 24V control power; when a transformer shorts or burns open, the entire control circuit goes dead — no thermostat response, no ignition sequence, and often a blown low-voltage fuse on the board. This 40VA rating provides the headroom needed for the furnace's two-stage control loads.

Specifications

Compatibility

Direct-fit replacement for the Tempstar T8MPT100J20B1 furnace and equivalent Heil/ICP models requiring a 40VA 115V-to-24V control transformer. Confirm primary voltage and VA rating before installing.

Installation Guide

1. Safety First - Disconnect power at the furnace switch and verify zero voltage with a multimeter.
2. Access - Remove the control-compartment service panel.
3. Document - Photograph the primary (line) and secondary (24V) lead connections before disconnecting.
4. Remove - Disconnect the wiring, then unbolt the transformer from its mounting bracket.
5. Install - Mount the new transformer and reconnect primary and secondary leads exactly per your photo.
6. Test - Restore power, confirm 24V across the secondary, and run a full heat cycle.

Signs You Need a Replacement

• No 24V control power; thermostat and board are completely dead.
• Repeatedly blown low-voltage control fuse.
• Burnt smell or discolored transformer windings.
• Measured secondary voltage reads zero or far below 24V.

Shipping & Returns

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