What are the specs for this Transformer?

The correct replacement for Tempstar model T8MPN125J20B2 — 115V to 24V | Ships Today is this exact part. It is the factory-specified replacement with exact OEM specifications. Using a part with different specifications can cause equipment damage or void your warranty. You can verify this by checking the data plate on your Tempstar equipment which lists the model number T8MPN125J20B2 — 115V to 24V | Ships Today.

Is this transformer compatible with Bryant or Payne systems too?

Many Tempstar parts are cross-compatible with Bryant and Payne systems since all three brands are manufactured by Carrier Global Corporation. The same physical part is often used across multiple brand labels with different model numbers. To verify cross-compatibility, check your Bryant or Payne equipment service manual for cross-compatible part numbers, or contact info@nationalhvacparts.com with your model number for confirmation.

Tempstar

Tempstar 40VA Transformer for T8MPN125J20B2 — 115V to 24V | Ships Today

Name: Tempstar 40VA Transformer for T8MPN125J20B2 — 115V to 24V | Ships Today
Brand: Tempstar
SKU: 1172810-GEN
Price: 24.95 USD
Availability: InStock

SKU: 1172810-GEN Brand: Tempstar

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Overview

This OEM control transformer, part number 1172810, supplies low-voltage power for the Tempstar T8MPN125J20B2 gas furnace. It steps the incoming 115V line voltage down to 24V and delivers 40VA of capacity to drive the control board, gas valve, thermostat circuit, and other 24V components. When the transformer fails — often from a shorted control wire or an overloaded circuit — the entire low-voltage system goes dead: no thermostat response, no ignition sequence, and no call for heat. A blown transformer is a frequent cause of a completely unresponsive furnace. This genuine OEM 40VA, 115V-to-24V transformer matches the original electrical rating and mounting for a direct, dependable replacement.

Specifications

Spec	Value
Part Number	1172810
Type	Step-Down Control Transformer
Primary Voltage	115V
Secondary Voltage	24V
Rating	40VA
Brand	Tempstar
Fitment	OEM Replacement

Compatibility

Direct-fit replacement for the Tempstar T8MPN125J20B2 furnace and shared-platform Heil, ICP, and Comfortmaker models that use the same 40VA 115V/24V control transformer. Confirm part number 1172810 and the 115V primary / 24V secondary rating before installing.

Installation Guide

Safety First — Disconnect power at the furnace switch and breaker and verify zero voltage with a multimeter.
Access — Remove the service panel to reach the control box and transformer.
Document — Photograph the primary (line) and secondary (24V) wiring before disconnecting.
Remove — Disconnect the leads, remove the mounting screws, and lift out the failed transformer.
Install — Mount the new transformer and reconnect the 115V primary and 24V secondary leads exactly per your photo.
Test — Restore power, confirm 24V across the secondary, and verify the thermostat and ignition sequence respond.

Signs You Need a Replacement

Completely unresponsive furnace with a dead thermostat
No 24V reading across the transformer secondary
Burnt smell, scorching, or discoloration on the transformer body
Furnace fails after a control wire short or component overload

Shipping & Returns

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

Shipping Information

Orders placed before 3PM CST ship same business day
Standard delivery: 2-5 business days
Express shipping available at checkout
Free shipping on orders over $75
Tracking number emailed upon shipment

Return Policy

30-day returns on unused parts in original packaging
Electrical parts (capacitors, contactors, control boards) are final sale once installed
Email info@nationalhvacparts.com to initiate a return
Refunds processed within 5-7 business days

Tempstar 40VA Transformer for T8...

$24.95

Frequently Asked Questions

Does this Transformer fit my Tempstar T8MPN125J20B2 — 115V to 24V | Ships Today?

Yes. This is the factory-specified OEM transformer for the Tempstar T8MPN125J20B2 — 115V to 24V | Ships Today. It is a direct drop-in replacement that fits without modification. Always verify the model number on your equipment nameplate before ordering.

How do I replace the transformer on my Tempstar T8MPN125J20B2 — 115V to 24V | Ships Today?

Difficulty: Medium (30–45 min)
Step 1: Turn off breaker. Step 2: Photo wiring connections. Step 3: Disconnect wires from old transformer. Step 4: Remove mounting hardware. Step 5: Install new transformer, reconnect wires matching voltage ratings. Step 6: Verify 24V output with multimeter.

My thermostat has no power. What failed?

Thermostat with no display = failed 24V transformer (or blown control board fuse). Check the 3A/5A fuse on the control board first ($1–$5 fix). If fuse is good but no 24V output from transformer, replace transformer.

Is this transformer compatible with Bryant or Payne too?

Many Tempstar parts are cross-compatible with Bryant and Payne since all three brands are manufactured by Carrier Global Corporation. The same physical part is often used across brand labels with different model numbers. To verify: check your Bryant or Payne equipment service manual for cross-compatible part numbers, or email info@nationalhvacparts.com with your model number.

Should I use OEM or aftermarket for my Tempstar transformer?

OEM recommended for reliability and warranty compatibility. OEM parts match exact factory specifications for proper fit, performance, and safety. While aftermarket alternatives cost less upfront, the risk of improper fit and reduced lifespan usually makes OEM the better value long-term.

How fast does National HVAC Parts ship?

Orders placed before 3:00 PM CST ship the same business day. Standard delivery is 2–5 business days anywhere in the continental United States. Express shipping available at checkout. We ship from Houston, TX to all 50 states. 30-day return policy on all parts.

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