We have just had a new central heating system installed . The previous system had 1mm twin and earth connecting the Thermastat to the boiler, however, on the new system , what looks like 3amp flex has been used to connect the Thermastat ( situated in Hallway) to the boiler ( situated in bathroom). The boiler is connected to the supply via a 3amp fused switch unit. Has the correct type of cable been used?