{"product_id":"tempstar-40va-transformer-for-t8mpt125j20b1-115v-to-24v-control-transformer-ships-today","title":"Tempstar 40VA Transformer for T8MPT125J20B1 — 115V to 24V Control Transformer | Ships Today","description":"\u003ch3\u003eOverview\u003c\/h3\u003e\n\u003cp\u003eThis genuine OEM control transformer (part number 1172810) steps line voltage down to low-voltage control power for the Tempstar T8MPT125J20B1 gas furnace. It converts 115V primary input to a 24V secondary output at 40VA, supplying the thermostat, gas valve, control board relays, and ignition circuit. A failed transformer is one of the most common causes of a completely dead control system: no thermostat display, no call for heat, and no blower response even though the furnace has line power. Transformers typically fail from age, a shorted secondary circuit, repeated overload, or a wiring fault that pops the internal winding. A burning smell, a tripped or open primary, or 0V at the secondary with line voltage present at the primary all point to transformer replacement.\u003c\/p\u003e\n\n\u003ch3\u003eSpecifications\u003c\/h3\u003e\n\u003ctable\u003e\n\u003cthead\u003e\u003ctr\u003e\n\u003cth\u003eSpec\u003c\/th\u003e\n\u003cth\u003eValue\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003ePart Number\u003c\/td\u003e\n\u003ctd\u003e1172810\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eType\u003c\/td\u003e\n\u003ctd\u003eStep-Down Control Transformer\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBrand\u003c\/td\u003e\n\u003ctd\u003eTempstar (ICP \/ Heil)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003ePrimary Voltage\u003c\/td\u003e\n\u003ctd\u003e115V\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSecondary Voltage\u003c\/td\u003e\n\u003ctd\u003e24V\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eRating\u003c\/td\u003e\n\u003ctd\u003e40VA\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFitment\u003c\/td\u003e\n\u003ctd\u003eOEM Replacement\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch3\u003eCompatibility\u003c\/h3\u003e\n\u003cp\u003eBuilt for the Tempstar T8MPT125J20B1 gas furnace and compatible ICP-family units (Tempstar, Heil, Comfortmaker) that use a 115V-to-24V 40VA control transformer. Confirm your original is rated 40VA before installing.\u003c\/p\u003e\n\n\u003ch3\u003eInstallation Guide\u003c\/h3\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cstrong\u003eSafety First\u003c\/strong\u003e — Disconnect power at the furnace switch and breaker, then verify zero voltage at the transformer leads with a multimeter.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAccess\u003c\/strong\u003e — Remove the furnace control-compartment service panel.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDocument\u003c\/strong\u003e — Photograph all primary and secondary wire connections before disconnecting.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eRemove\u003c\/strong\u003e — Label and disconnect the leads, remove the transformer mounting screws, and lift out the old transformer.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eInstall\u003c\/strong\u003e — Mount the new transformer, reconnect primary (115V) and secondary (24V) leads exactly per your photo.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTest\u003c\/strong\u003e — Restore power and verify 24V across the secondary terminals and a normal call for heat.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch3\u003eSigns You Need a Replacement\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eNo power to the thermostat or control board\u003c\/li\u003e\n\u003cli\u003eFurnace completely unresponsive despite line voltage present\u003c\/li\u003e\n\u003cli\u003eBurning smell or visible scorching on the transformer\u003c\/li\u003e\n\u003cli\u003e0V at the secondary with proper voltage at the primary\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eShipping \u0026amp; Returns\u003c\/h3\u003e\n\u003cp\u003eShips same day before 3 PM CST. 30-day returns. Backed by the National HVAC Parts fitment guarantee.\u003c\/p\u003e","brand":"Tempstar","offers":[{"title":"Direct Replacement","offer_id":63021702938995,"sku":"1172810-GEN","price":24.0,"currency_code":"USD","in_stock":true},{"title":"OEM","offer_id":63048405614963,"sku":"1172810","price":31.2,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0984\/1190\/5395\/files\/nhvac-transformer-control-1172810_1946ac06-4716-4180-b701-34cb042a3e06.jpg?v=1782958336","url":"https:\/\/nationalhvacparts.com\/products\/tempstar-40va-transformer-for-t8mpt125j20b1-115v-to-24v-control-transformer-ships-today","provider":"National HVAC Parts","version":"1.0","type":"link"}