I have recently had a nest learning thermostat (3rd gen) installed. My heating system is a conventional (also known as heat only) one and has a separate hot water tank.
When I set up the thermostat, I selected the system heating option. Everything works fine other that a slight issue with the hot water.
When the hot water is called for by the thermostat, the boiler heats up the water and the circulating pump in the airing cupboard powers on. Eventually the boiler stops heating the water as the thermostat on the hot water tank says it is satisfied, however the pump continues to run for the remainder of the hot water schedule, it doesn't power off.
It doesn't do this with the central heating however, once the central heating is up to temp and hot water is off, the boiler stops heating and the pump powers off after a brief overun period. I have turned bacteria protection off and this doesn't seem to change anything.
Is it normal for the pump to continue running throughout the hot water schedule???