Sounds like a coolant temperature sensor problem. Has the van been running smoothly or smoking more than usual? (These are other symptoms SOMETIMES witnessed with the sensor problem.
Had a similar thing on mine a whole ago. Easy fix.....new sensor and a coolant top up will see you sorted.
There are two sensors and it is usually the 4-pin sensor that plays up and the colours seem to vary so don't be surprised if VW supply you with a different coloured sensor......so long as the part numbers are correct it'll be ok.
2-pin (green) = 059 919 501 A
4-pin (blue) = 701 919369 C
The reason the 4-pin is usually at fault is because it is this sensor that feeds the ECU and temperature gauge with temperature info.
http://www.volksbits.co.uk/servlet/the-7574/COOLANT-TEMPERATURE-SENSOR-VW/Detail
They are mounted on the front of the engine block between injectors 1 & 2. Remove the metal wire loom retaining clip and then there is a small plastic C-shape retaining clip that slides out. Simply remove the sensor then, but make sure the rubber O-ring comes out as well.
There is plenty of info regarding this on the forum if you use the "search" function!