# Mitsubishi electric mini-split / thermostat error



## covenstine (Jun 5, 2021)

Hello, 
I am seeing an error code that is otherwise unlisted on the wireless MRCH1 thermostat, which connects to a ducted Mitsubishi electric unit in the attic.
The display just reads "E 27"
The second zone for the first floor is run by a Mitsubishi Mr Slim unit, which is working fine.
None of the documentation we can find- online or otherwise- lists error 27, so we're scratching our heads on this.
The client says it was working last weekend, and of course, here comes a heat wave.
I've done a visual inspection of the unit and nothing stands out- power cycling the system & thermostat doesn't help, as the error code returns as soon as a button is pressed.
Any thoughts?
Thanks!


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## beenthere (May 30, 2009)

Indoor/Outdoor communication error.


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## covenstine (Jun 5, 2021)

covenstine said:


> The display just reads "E 27"


FWIW, to save anybody else the headache, this is not an indoor/outdoor communication error.
Per the additional documentation available from Mitsu/Honeywell, this code means that the thermistor is out of range.
This can be caused by:
the ambient temperature the thermostat is reading is over 90 degrees F, OR
the thermistor is faulty and the thermostat needs to be replaced.

It should be noted that after several days, when the ambient fell to under 65, the thermostat behaved normally, and occasionally in the following weeks, instead of "E 27" the display could just read 'wait,' which probably should have been a give-away after 5 minutes that the thermostat was bad.
Hope that helps somebody!


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