HMO bills included

HMO Licensing

Hi, I have an HMO where I let out the rooms individually. This is the first time doing in this way, so I have a question. In the rent-a-room agreements, it states a bills cap for the whole house (as can't be done per room as communal lounge and kitchen). They have given me the hours they want but how do I do it if they change the times on the thermostat or increase the temperature so much that it doesn't switch off at temperature reached on thermostat? I am trying to work something that is fair rather than someone in a situation where it is abused and the others are responsible for costs. Any advice or guidance on this, would be much appreciated. FYI, at the moment I have internet access to the boiler so can see timer and set the times, although this can be changed by the thermostat at the house too.