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If the treadmill was disassembled and reassembled in the least for storage, then you should check all aspects of its assembly and reassembly in detail and with care.
Re-seating all connectors, period, (-with the power Off!) would be ideal if the storage it was in was the least bit of either damp or dusty or both.
Would you like to try a reset of the console?
Well, I had an additional thought. If it was stored for several years, and if it is the sort of console that has internal batteries, then you would probably (in that case) have to replace the batteries.
Check for a battery hatch.
The general result of my research is, that you can recalibrate the incline, but there is no console reset as such.
I know the model, yes, thanks.
The console may simply be gone-bad. It is admitted to be a frequent problem with this model, the C2100.