Timer system for Immersion water heater?

I moved into my present address 3 years ago but I have never had an instruction manual for my water heater , the former tenant failed to leave one behind when she left. The only markings on the timer-box are: HORSTMANN ELECTRONIC 7 MAXISTORE . It was only a wild guess on my part to feed the above name's into my computer and I was very surprised to find your page. I am an OAP of 70yrs. so these thing's dont come easy at our age.Due to high elect.bills I want to reduce the times my heater come's on. Thanking You ,