Yes, of course! The effect would be fairly negligible because you'd only have the hob on for a few minutes to boil a kettle, but for the purposes of this you can consider the house a closed system, if it required X amount of energy to heat the house by 10degrees (for example) and the only heating in the house is the central heating boiler then that will have to provide X to heat the house that much, if you have a hob providing Y amount of heat then the boiler will have to provide X-Y to heat the house that much, if you had a light bulb that produced Z amount of heat on too then the boiler would have to provide X-(Y+Z) to heat the house by 10 degrees....
It a pretty basic law of thermodynamics.