I've not got a solution Steve, since the MR850 is usually reliable (however prone to being dropped) but I know that there have been a few different software versions applied to the MR850 that have enhanced and modified the way it works, including the self-diagnostics and heater-wire compensation. Have you got the latest manual Steve? Revision "H" I think. Perhaps the error-code is listed in one of the revisions.

Unfortunately I don't have any manuals at hand since I'm on leave but no doubt you've already looked to the device configuration, test-setup, consumables and the heater adaptor wire and dual temp/flow probe as a potential source of problems and substituted them to make certain. Was the problem with dual heater-wire operation or single, intubated or non-intubated, what gas flow-rates, humidity compensation, etc? Will the machine run diagnostic checks 1-6 and can you enter the other diagnostics and configuration menus?

The advice given by the F&P technical support is usually very good and the engineers there are very informative. The MR850 PCBs always come as a pair since they are manufactured and calibrated together I think. The MR850 is usually a reliable piece of kit and the only problems I find are that the heater-wire adaptor socket connections and the dual-flow socket connections sometimes suffer from poor solder joints or the sockets need replacing after drop-damage with plugs being connected plus case changes.

The PCBs are predominantly surface-mount components in any case so if you've eliminated the possibility of heater-wire, dual-temp/flow probe, obvious internal connector or fuse problems and checked the function/suitability of the test-circuit and consumables you're using plus the unit is configured, used and setup correctly for testing purposes, then replacing the PCBs (or decommissioning) may be necessary. Do you use the F&P circuits by the way?