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

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