Heathrow operate small "hoppa" buses to take you to the airport hotels but they are quite expensive for what they are. However under an old agreement all bus travel within the surrounding area of the station is free from the Central Bus Station. You just step on the Red London Bus and get off at Nene Road bus stop for the Park Inn which is a two minute walk away. Similarly coming back there are busses to Heathrow Central from the other side of the road. You might want to get the hoppa bus there but then use the London buses once you have got your bearings.