There are a couple of threads covering bus options from t4 to t5

The bus stops at t4 are in link in this post

H30EM early morning employee bus between T4 and T5

You will need to click on 'map view'.

This stop has the free bus (H30) and the london buses. As KARFA and corporate-wage-slave mention there is a stop nearer the hotel which is only served by the london buses

There is a lot of other useful info in that thread