Glad the reset seems to have done the trick.
Got me worried so that's why I checked for the silica bag, as it's something I've been meaning to do.
For anyone who's interested in checking to see if there's a bag in the expansion tank, its difficult to see until you actually syphon the antifreeze out the expansion tank, then you can see it in the top left.
I clamped off the bottom feed pipe just in case the bag split whilst trying to get it out.
Gonna try the reset in the morning for no other reason than to make sure mines correct.