Electric Immerser

[debi2000]

i have an electric immerser, which normally stays switched on all day, from about 10am until 11pm. just been talking to someone who says this will cost me a fortune. i thought it would cost more in electric bills to switch it on and off throughout the course of the day. can someone help me please as i have just moved into my first flat and am a bit clueless when it comes to these kind of things. thanks

[buildersmate]

With electricity, ALL the energy used gets converted into heating the water. This is unlike a gas or oil-fired boiler where 'cycling' the boiler on/off a lot causes inefficiency - because the boiler has to keep heating up and it is less efficient at converting fuel into heat until at working temperature. So it isn't gaining you anything by leaving it on.
An immersion heater has a thermostat so once the cut-off temperature is reached by the water, it will cease to consume electricity. It will then only switch on again (unless water is drawn off) when the heat losses to the cupboard around the tank have resulted in the tank cooling down again. So your strategy isn't a total disaster.
However, peak electricity is one of the most expensive forms of energy known to man, so make sure your tank has loads of insulation around it, and better still, enquire about having an Economy 7 meter fitted so you can heat the tank at night using cheaper off-peak electricity prices.