How to reset Boss Thermostat BRTRF that lost communication?

Had a power cut last night and now thermostat wont work and boiler wont come on for heating only for hot water. The lights on the main part of the thermostat (fixed to wall by boiler)wont stay on even though Ive tried pressing the reset button nothing is working. Please help as have 84 year old with dementia here and its freezing.