If you find that you have no hot water. one of the first checks to do is to see if your unit is hot to touch.you will find that by touching the fill elbow at the top of the cylinder. this will give you a safe gauge of the tempreture of the cylinder. If cold move on to the source of the heat for your unit . in this case it is the immersions.
your unit is hot to touch. so you will have to check the water level. which will need some tools to remove the blanking plug to top up the cylinder.if you have to top up the water level. i would recomend a service to trace where the water has gone.if water level fine move onto the pump.
The immersion's can be located at several locations on your unit .depending which type of unit you have. you firstly have to ensure that the power to the unit is turned off . Then remove the black plastic housing. you do this by undoing the nut . You then will see two stats( the black/maroon stat is the control stat which should be set at 70o/c. the red stat is the trip stat which is set at 90o/c. you will notice that there is a small black reset tab. you may find by pressing lightly you may here it click. if it does this then you may find that your unit will start heating once you turn the power back on. if the it doesn'click then the fault may lay somewhere else phone for a service.