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Editor’s Note: We spent a lot of time in back and forth with Corsair and did receive two separate units for test which gave us the same disappointing results. Corsair did finally communicate this to us.

Corsair: Last week were able to duplicate your findings by restricting the airflow to the power supply and because of this have implemented rolling changes to the RM that will allow the fan to turn on sooner if such a condition occurs. As you know, the RM Series PSUs are backed by our 5 year warranty. If a user does experience an issue, we will have their PSU replaced, no questions asked and at no cost to them.

Editor’s Note: Corsair has publicly addressed this concern as linked below.

Corsair Blog: Potential thermal issue with RM750 and RM850 products

Corsair Forum: Potential thermal issue with RM750 and RM850

The Corsair RM series power supplies are designed to run without active cooling for up to 40% load at typical room temperatures (25°C, or 77°F) and are capable of continuously outputting 100% of output capability at ambient temperatures of up to 40°C (104°F). We have found that our power supplies are typically used in environments much lower than 40°C and tend to have some natural aspiration within the chassis that allows for some air movement, such as from a nearby graphics card or chassis fan, within the PSU housing, when temperatures exceed normal room temperatures. We have found that this normal aspiration can maintain Corsair’s Zero-RPM fan-less mode even at temperatures as high as 35°C (95°F) when only at 40% load for durations of up to 15 minutes.

Thanks to recent feedback provided by an early reviewer, we have discovered a PSU fan operation issue that can be triggered with the RM750 and RM850W under highly unusual operating conditions. For the issue to occur, the PSU must be run for more than 15 minutes at:

Ambient temperature 35°C (95°F) or higher

Zero ambient airflow, i.e. no airflow provided by system fans or by fans on other components

Under these conditions, impacted PSUs may shut down before the cooling fan starts spinning. This shutdown will cause no damage to the PSU or the system. As these conditions are extraordinarily harsh, we believe most users will not be impacted. If you feel you have a unit that has been impacted, we are offering advance replacement returns for the PSU, with Corsair paying all freight costs. Please click here for instructions on how to obtain a replacement unit, or to ask any questions.

Editor's Note II: Corsair has verified changes made to RM units that would address the shutdown issues we experienced. These changes would very likely earn the Corsair RM series at the very least a "HardOCP PASS."

The RM Series PSUs, like all Corsair PSUs, are designed and tested using methodologies that closely simulate the environment of an enthusiast/gaming PC under heavy, sustained workloads. Our testing has proven that the cooling system of the RM Series will engage and provide the necessary cooling during heavy real world use.

That said, we’re enthusiasts, too. We understand why Kyle and Paul came to the conclusions they did, and based on their feedback, we’ve implemented a design change that will allow our RM Series PSUs to go the extra mile and endure the extreme synthetic test conditions of the HardOCP test lab.

We have changed the value of the resistor between the thermistor and the fan controller so the fan turns on much sooner than the temperature that would trigger OTP. Therefore the fan should always turn on before OTP is triggered; preventing the PSU from shutting down before it is necessary.

This change has been implemented in all RM PSUs produced since mid October. While we honestly believe even extreme users will never run into the issue encountered during HardOCP’s synthetic test, those end users that want to know if their RM can endure HardOCP’s torture test can identify the updated PSUs by a lot code of 1341 or higher.