Hi There
Well it must be a common problem as ours did the same last weekend.
If air is in the system the sender can be damaged ! so change it before refilling with antifreeze and bleeding (will save you money) see bottom of page for part number etc.
Here are the fixes though!
1- have you lost water recently or let any air in the system?- If yes the 1st thing you need to do is drain the system and refill as per manual with 50 / 50 mix of water & antifreeze. Be sure to bleed the system as below--
Bleeding-
1 remove top grille
2 remove the air valve (13mm spanner reqd)
3 open the bleed valve on the thermostat in the engine bay (be careful as this is fragile)
4 remove the expansion tank lid (blue screw cap normally)
5 fill the tank with 8 ltrs of antifreeze followed by water (at this stage run engine and get a helper to keep topping expansion tank up until full to top.
6 Rev engine to 2000 rpm until water WITHOUT bubbles runs fron the rad bleed valve at front and then replace the plug.
7 ensure expansion tank is full and replace top.
8 Close bleed valve on thermostat housing and stop the engine.
Almost done now!
Now part 2 (which must be done also)
9 Raise the front of the van 400mm (jack it up or drive it up a big bank)
10 Uuscrew the radiator bleed screw (13mm spanner) again but this time only 3 turns.
11 Undo the thermostat bleed valve again
12 remove the expansion tank lid again and be ready to top up
13 run the engine at 2000 rpm again until water flows from the rad screw (NO air bubbles must be visible)
14 close the rad valve screw (13mm Spanner)
15 top up expansion tank again until full
16 replace expansion tank top
17 close thermostat valve and stop engine.
18 fill the feed tank (the one in the back access via number plate with antifreeze to max level)
19 Run the van until hot-
20 Job Done
If that does not work its the sender to the rear of the thermostat housing that is duff. Part number 93492 from any GSF depot at £5.60!
Remember that you will need to bleed and refill the system after fitting as detailed above. Hope that helps?
Darren