Not replaced during the day but just cooling down naturally - boil a kettle and leave it for 12 hours and the water gets cold.
There should be a timer/programmer somewhere in the property. A 3am start is odd - unless it's on some cheap rate night time programme. Is there an immersion heater doing the heating or a regular boiler?
If you have a landlord look to him for help - if it's your own place then you're the landlord!
Peccavi
July 2009