I ride a 2013 F800GS. I have heated grips, sorta (as of late). I was riding a few days ago and they worked just fine, nice and toasty... Then at some point my I noticed my hands a little cold. On stage 2 they work as advertised, for stage 1. The grips are warm. On stage 1, with no gloves on, I can feel some warmth. Attached to the GS911, on stage 1 the 'heated grips' line on the PC app shows on/off cycling about every 1/2 second, stage 2 shows on steady. My question is, what would be the culprit of failure like this, they don't get hot anymore, just stage 1 warm on stage 2. GS911 doesn't report any failures. Thanks.
Check you battery condition and the charging voltage.
F800GS's are known for burning out their alternator stators. 2013 should be ok as i think you have the updated stator and flywheel, but check it anyway.
Battery condition is also critical. If it is still the original battery, it may be time for a replacement.
When the battery voltage or current drops off, things like headed grips are automatically turned off on the F800, or at least cycled on/off to alleviate the load.
Battery was fresh from the store last year and on a tender all winter. Voltage is a ~13.5 engine running, and 12 off. I feel like its a faulty controller but can find no information about that system. Like I said it works, sorta. just cant get real heat from them.