How much does gas central heating cost to run per hour?

macman

The max rating on the boiler might be 35kW, but it doesn't run at anything like that in CH mode. It would only run at peak output for DHW.
As I pointed out before, it's very simple to calculate from gas usage over an hour or a day, but it won't tell you anything useful, because the weather is so variable. As the ambient outdoor temp falls, the rate of heat loss increases, and the boiler will ramp up to maintain the set temp-which could br anything from 17C to 23C. A 1C variation could increase your gas usage by 10%.