Since having the combi fitted my electricity usage has shot up. Gone from an average of 163kwh a month to 340. So even though gas usage is down a lot, electric going up means its costing us more. Excuse my rough maths but i have the boiler on for approximately 52 hours a week, so if it was indeed running fully for those 52 hours thats about 210 hours a month. The boiler power usage says 137w. So 28.8kwh a month i think would be the max, but its gone up 158kwh last month.