--- title: "Middleby Marshall HIGH TEMP ERROR: every thermocouple has dropped out" description: "What HIGH TEMP ERROR means on Middleby Marshall HIGH TEMP ERROR: every thermocouple has dropped outs, what to check before booking, and when it is not a failure…" url: "https://pizzaovenrepair.center/error-codes/middleby-marshall-high-temp-error/" --- # Middleby Marshall HIGH TEMP ERROR: every thermocouple has dropped out On the PS638 the message means every thermocouple probe has failed open, so the control has no temperature reading at all. ## What HIGH TEMP ERROR actually means. On the PS638 the message means every thermocouple probe has failed open, so the control has no temperature reading at all. The PS640 gas manual adds that a PLC malfunction can cause it. The X-Series shows the same condition as ALL PROBES OPEN, with an alarm. Middleby Marshall pizza oven display · also shown as High Temp Error, ALL PROBES OPEN What to do when HIGH TEMP ERROR shows on the pizza oven ### Kind of code Temperature and sensors A probe is handing the controller a reading it cannot believe, or none at all: a deck or tunnel sensor coated in baked-on flour and grease, its lead chafed or scorched where it passes the heat, or a connector loosened by years of doors slamming. The oven then runs hot, stalls short of its setting or shuts the heat off to protect itself. Letting the oven cool and restarting it is reasonable; a sensor that still reads wrong sits behind a panel, and that is a visit. ### Usually leads to Pizza oven thermostat and control repair Thermostats calibrated or replaced, probes, timers, boards and displays repaired, so the pizza oven holds the temperature the cooks set and shows the right number. ### Shows up as Pizza Oven Error Code on a Deck, Conveyor or Rapid-Cook Display A pizza oven error code shows as letters or numbers on the display of a conveyor, deck or rapid-cook oven, a flashing light on its panel, or a message about ignition, heat, belt or airflow. ### Make Middleby Marshall A Middleby Marshall conveyor call is about the line: how many pies came out right before the belt slowed, stalled or the crust went pale. ### Source Middleby Marshall PS638 electric and gas oven owner's operating and installation manual (74617 Rev G) PS638 (74617) and PS640 gas (60251 Rev J) touch screen ovens print HIGH TEMP ERROR. X70G, X55G and X55GWB print ALL PROBES OPEN for the same event. ## Before you book, in this order. Each step comes from Middleby Marshall's own guidance for HIGH TEMP ERROR on its pizza ovens. Follow it to the end: the last card says whether this is a visit. 01 Stop baking: without any probe reading the oven cannot hold a temperature. 02 On an X-Series, press Dismiss to silence the alarm, then turn the oven off. 03 Book a visit so the thermocouples, their wiring and the PLC can be tested. ### Still there? It usually turns into [pizza oven thermostat and control repair](https://pizzaovenrepair.center/services/pizza-oven-thermostat-and-control-repair/). Book with the code and the model number. ### What not to do The name suggests an overheat, but the cause Middleby Marshall lists is lost probes or the PLC. A single failed probe on an X-Series shows PROBE # OPEN instead and lets the oven keep running. ## What you may notice with it. The pizza oven problems HIGH TEMP ERROR tends to arrive with. Answer these at the pizza oven before anyone is booked. [All problems](https://pizzaovenrepair.center/problems/) Before you call ### [Pizza Oven Error Code on a Deck, Conveyor or Rapid-Cook Display](https://pizzaovenrepair.center/problems/pizza-oven-error-code/) [All 7 causes, cheapest first](https://pizzaovenrepair.center/problems/pizza-oven-error-code/) It also comes with - [**Pizza Oven Not Getting Hot Enough to Bake a Crisp Crust**](https://pizzaovenrepair.center/problems/pizza-oven-not-getting-hot/) Problem ### Pizza Oven Error Code on a Deck, Conveyor or Rapid-Cook Display 7 causes, cheapest first Where HIGH TEMP ERROR usually leads ## Pizza oven thermostat and control repair. **Thermostat calibrated or replaced, temperature probe, timer, controller board or display · moderate.** Book a visit [What the job involves](https://pizzaovenrepair.center/services/pizza-oven-thermostat-and-control-repair/) ## Middleby Marshall pizza ovens. A Middleby Marshall conveyor call is about the line: how many pies came out right before the belt slowed, stalled or the crust went pale. [Middleby Marshall pizza oven repair](https://pizzaovenrepair.center/brands/middleby-marshall/) More Middleby Marshall codes [RESET IGNITION](https://pizzaovenrepair.center/error-codes/middleby-marshall-reset-ignition/) [HEATING ERROR](https://pizzaovenrepair.center/error-codes/middleby-marshall-heating-error/) [PROBE # OPEN](https://pizzaovenrepair.center/error-codes/middleby-marshall-probe-open/) [FRONT BELT JAMMED](https://pizzaovenrepair.center/error-codes/middleby-marshall-front-belt-jammed/) [REAR BELT JAMMED](https://pizzaovenrepair.center/error-codes/middleby-marshall-rear-belt-jammed/) [FRONT BELT COMM LOST](https://pizzaovenrepair.center/error-codes/middleby-marshall-front-belt-comm-lost/) [SENSOR OPEN](https://pizzaovenrepair.center/error-codes/middleby-marshall-sensor-open/) [MAIN BLOWER ERROR](https://pizzaovenrepair.center/error-codes/middleby-marshall-main-blower-error/) [Combustion Blower problem](https://pizzaovenrepair.center/error-codes/middleby-marshall-combustion-blower-problem/) [**00FF](https://pizzaovenrepair.center/error-codes/middleby-marshall-00ff/) [CLEAN FILTERS](https://pizzaovenrepair.center/error-codes/middleby-marshall-clean-filters/) [CONTROL OVERTEMP](https://pizzaovenrepair.center/error-codes/middleby-marshall-control-overtemp/) [All 16 Middleby Marshall codes](https://pizzaovenrepair.center/error-codes/#codes-middleby-marshall) Temperature and sensors on other makes [Fontana Forni Er1](https://pizzaovenrepair.center/error-codes/fontana-forni-er1/) [Marra Forni Open](https://pizzaovenrepair.center/error-codes/marra-forni-open/) [TurboChef F2](https://pizzaovenrepair.center/error-codes/turbochef-f2/) [Wood Stone open](https://pizzaovenrepair.center/error-codes/wood-stone-open/) [All 15 codes of this kind](https://pizzaovenrepair.center/error-codes/#family-temperature) Middleby Marshall builds this ### Conveyor and rapid-cook pizza oven A tunnel oven whose wire belt carries pizzas through hot air jets, and the countertop rapid-cook ovens that bake a pizza in minutes. ## In Middleby Marshall's own words > All thermocouple probes have failed [Middleby Marshall PS638 electric and gas oven owner's operating and installation manual (74617 Rev G)](https://www.middlebymarshall.com/wp-content/uploads/2021/07/74617-PS638-Owners-Manual.pdf) [Middleby Marshall PS640 series gas oven owner's operating and installation manual (60251 Rev J)](https://www.middlebymarshall.com/wp-content/uploads/2022/08/PS640G-IO-Manual-60251-Rev-J_NEW-2025.pdf) [Middleby Marshall X70G, X55G, X55GWB gas oven owner's operating and installation manual (78866 Rev F)](https://www.middlebymarshall.com/wp-content/uploads/2021/05/X55-X55GWB-X70-78866-Rev-F.pdf) Every code on this site is taken from the manufacturer's documentation, never from a forum or a parts listing. PS638 (74617) and PS640 gas (60251 Rev J) touch screen ovens print HIGH TEMP ERROR. X70G, X55G and X55GWB print ALL PROBES OPEN for the same event. ## Middleby Marshall HIGH TEMP ERROR pizza oven repair, where we come out. The same visit in every metro below: the code, the model number, and a diagnosis before any part is ordered. 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Stop baking: without any probe reading the oven cannot hold a temperature. If it comes back, it needs a visit. ### Is my Middleby Marshall PS638 overheating when it shows HIGH TEMP ERROR? Not according to the manual. It means all the thermocouple probes have failed open, so the control cannot read the oven temperature at all. ### Why would every probe fail at once on a PS640? Several probes rarely die together. A shared connection, the wiring harness or the PLC that reads them is more likely, which is why the PS640 manual names the PLC too. ### Is ALL PROBES OPEN on an X55 the same problem? Yes. The X-Series gives the same cause, all thermocouple probes open, and asks for immediate repair. --- **[Read on the site: Middleby Marshall HIGH TEMP ERROR: every thermocouple has dropped out](https://pizzaovenrepair.center/error-codes/middleby-marshall-high-temp-error/)** **[Book a visit with PizzaOvenRepair.center](https://pizzaovenrepair.center/schedule/)**