2007 honda nss 250 reflex. When I ride at 50 mph temp ok. When i slow down to 25, temp starts rising above normal. With engine shutoff, coolent boils. I leave ignition switch on until fan stops. I bought used so I don't know history but this is new problem.

 

I can't speak to the 250's but on many bikes the fan will run after ignition is shut off to prevent coolant "percolation" since the water pump isn't spinning once you shut the engine off. If its percolating could definitely be low on coolant and causing your problems.

 

if the bike is getting hot just riding somewhat slow I'd say its low on fluids, both oil and coolant. if there isnt enough of it, even if the rest of the engine is able to circulate the fluids, there wont be enough throughout the system causing air pockets that just heat up the bike over normal temps. id suggest a full service of the bike since you dont know its history, and go from there.