Coolant low, then high and no heat.
 

Hi guys, so I recently did a long trip (about 300 miles), 200 miles into the trip a warning message came on to check the coolant level, I pulled over, check and sure enough it was bellow the min line (only just in the reservoir), I let it cool down and then toped it up to the min line (just so I'd know if it had lost anymore when I next checked. Anyway, when I arrived at my destination I had a look and I'd actually gained coolant, to the point that it was well over the max. I drove home fine but now I don't have any heat in the cab. I have searched around on line for a bleed valve but no dice. I have followed a YouTube videos advice and ran the engine up to temp with the coolant cap of (sat there for 45 minuets) but that's made no difference. Has anyone ever experianced this before and if so... what was the fix? Cheers

Matt.