Your Heat Interface Unit (HIU) has a “Keep Warm” facility. This is to make sure that the hot water plate heat exchanger is kept warm, so that as soon as you want to use your hot water the HIU can provide a fast response and make sure that hot water is available to you instantly.
The 'Keep Warm' facility uses a small amount of heat, which is the usage you will have seen whilst you were away.
As well as making sure that hot water is available to you instantly, maintaining a constant trickle through the HIU helps make sure that there is no hot water stored in the system which could lead to a legionella risk. So it is also important for health and safety reasons that the ‘Keep Warm’ facility continues to work even when your home is unoccupied.
The cost of this 'Keep Warm' facility is under £2.00 per month.