Question

I have a fiat joint van 5 years old have just had first run of the year and the water pump stays on all the time can only turn off by computer pad is this frost damage to the pump

Answer

No, this will not be frost damage. The pump is OK, it is the mechanism that controls the pump that is the problem. if you have microswitches in the taps then it is probable that one of these has gone short circuit. you will need to cut the wire to the microswitches in turn (if you have more than one tap) to identify the faulty switch.
If you have no microswitches then the pressure switch, either attached to the pump, or in the cold water feed pipe, may need adjusting or has a fault.
Please advise the make of your water pump if you need further information.