Could anybody tell me what it costs to run a gas boiler for 1 hour?
check the manufacturer website. really depends on the age of boiler, temperature settings, state of your overall system.
Moved to Plumbing & Heating
It depends on a lot of variants, boiler, system, heat loss of building, etc.
Take a meter reading, turn on boiler for one hour. Take another meter reading. This will give you m3 of gas used. 10.8kwh in 1m3 of gas. Then multiply by your charge from your supplier per kwh. This will be on your gas bill.