How to get a better temperature bath in cold weather Ideally what we all expect when running a bath is to fully open the hot bath tap and receive an instant supply of hot water. In most instances, this will be the case, unless a fault occurs to disrupt the smooth operation of the hot water process.  Hot water can be generated separately using a different source of energy to the heating system,  on some systems both heating and hot water is incorporated together using a single source of energy, ...