Hi, We are a couple living in a rented 3 bed house with a boiler and tank equipped with an immersion heater, both located in the loft. My elec bill for the 6 weeks to Oct 9th is quite high (£121 for 970 units) and I suspect it's because of the way I set the immersion heater. We have a thermostat in downstairs and a timer (one for CH, one for DHW) in the old airing cupboard. Also in this cupboard are two switches, one for the boiler and one for the immersion heater. The CH timer has it come on twice a day, 2 hours in the morning and 5 hours at night (assuming the thermostat is tripped by a low temp). So far so good. The DHW at the moment though is only on for about 20 minutes per day, just before we wake up. We take a shower each/day on average, and sometimes less than that (because we shower at the gym, not because we're filthy ). I'm not familiar with the immersion heater logic. Does it come on to maintain a certain temp in the tank? In which case should we have the DHW timer stay on longer so as to use gas instead of elec? How long for?And does the tank get topped up with cold mains water as it is depleted by DHW demand? Thanks for any help.