I've had a Vaillant Ecomax 828E LPG combi boiler for just
over a year now, in my 2 bedroom chalet bungalow. The house
used to have oil-fired CH, but I changed it to LPG when the
old boiler packed up.

On oil, it used to cost between 500 and 600 pounds a year to
heat the house and the hot water.

Even that is horrendous. Do you leave the windows open or something? If not,
you've got a really serious lack of insulation problem here. Heating to only
18C and using little hot water, your bills should have been half that, or
less. Get your insulation checked ASAP. Ensure your hot water cylinder has a
thermostat that actually cuts the gas.

Christian.