Your main supply of hot water should be provided by the bottom immersion heater, which I guess would be on the timeclock to run at night on off-peak electricity.
The possible reasons for no hot water are:
There is no power from the off-peak supply (switched off, fuse gone etc) Check that the lower red neon comes on v late at night (prob. after 12.00)
The immersion element has failed (need new one fitted)
The timeclock has failed (need new one). It is possible after all this time that the backup battery has failed and the clock is not working as it should. Is it running and showing the correct time?
The overheat sensor in the immersion has tripped (needs to be manually reset). But this would happen because of another problem somewhere.
And there are no doubt other reasons I haven't thought of!!
In the meantime you can press the 'boost' button on the timer, which should give you the top half (ish) of the tank full of hot water. May need to press it again after an hour has elapsed. You will need to do this at least daily. It will use electricity at peak rate.
If you are competent with electrics, and have a multimeter and know how to measure resistance, you could isolate the supply, take the cover off the lower immersion, and measure the resistance of the element, which should be about 20 ohms. If it is, some of the other avenues I mention will need to be explored.
Otherwise it's probably time to get a professional in.
