I found it, the answer.
I have Danfoss HPa2 actuators, and the heating one is fine but the water one is at fault.
When the timer cuts in, it opens the valve as required. However, when the timer/programmer cuts out, the actuator closes off as far as the power is concerned, but it seems the internal motor and the plastic spindle that fits over the valve head are not connecting in 'the turn off' mode, and although the switch is cutting off, it is leaving the valve open. Until you take off the actuator and put a screwdriver in the actuator and turn the spindle back to 'valve off' mode and turn the valve itself back to off, the water will keep running.
I found it by using the manual level on the actuator and the lever is not returning to the off position even though the power is cutting off, so essentially it is leaving the valve open and all the time the heaing is on, the water in the tank is also being heated. The thermostat is fine, and thinks it is turning off the water valve but if course, it is still open all the time.
I have ordered a new actuator, and hope this will do the trick! I do appreciate your help, and you can add this one to your experience in case anyone else asks again.