thumper80

2017 RR, I do think it was all caused by the thermostat failing though, couldn't be certain how long it wasn't working for so could have been a while as it never blew steam out it just trickled a bit of coolant out of the pressure relief valve next to the filler cap on the radiator

Probably the thermostat, test it as mentioned above, it happened to me too but also whip off your water pump cover and inspect the water pump impeller too, the fins on mine disintegrated due to the excessive heat, i replaced mine with the CSP aluminium impeller kit bit pricy at 50quid but gives me piece of mind if my thermostat ****s itself again. Goes without saying you'll have to replace your coolant too it goes very grey after a while anyway so probably due a change, remember to crack the air bleed bolt on top of the cylinder and leave an air gap at the top of the radiator when refilling so there is a little room for expansion otherwise it may build up too much pressure and blow past the impeller shaft seals.