As I can = remember there is third sensor for this pump.  I don't have Bentley at hands now so I = can't be sure.  If there is it = might be bad..or the other alternative is.. this pump is located at highest point of = engine compartment and there could be an air bubble and coolant doesn't = circulate at all => sensor says to pump it's hot still here just keep on = pumping.  Test if the one or both hoses of this pump are cold after drive..if yes = => there is an air bubble.
 
Check this first.
 
Juha Koivisto
88 Vanagon (Caravelle) 1,6TD (old = school bus with 9 seats)
TURKU, FINLAND