Take a look at our range of hot water systems -. Boiler on the blink? think help-link! Look at the following table that compares two types of combi boilers and their running costs the numbers are considered for a 3 bedroom-flat with 4 residents the annual costs were calculated with a presumption that 1 kwh of gas costs 4.38 pence and 1 kwh of electricity is 13.58 pence. I noticed our boiler was making some strange noises each time it started up lately a friend.