Water heating up even when set water heating set to off on Tado app

Hello all,

I have recently bought a house built in 2004 by Barratt Developments in Greater Manchester area.

There is a Potterton boiler in the kitchen and a cylinder on the third floor with an immersion heater.

Please see attached photos.

The previous owner installed the tado smart thermostat and Tado works to control the heating throughout the house (after a lot of help from forum members) .

I have been experimenting with the hot water in order to find the most economic usage and I have a rather strange problem.

I switched off the immersion heater on the cylinder using the switch in the cylinder cabinet and set the hot water to off in the tado app four days ago after heating up the water for one hour. My wife and I have each had showers for about ten minutes each every day and used the hot water for washing up and so on. However the water just seems to keep on staying hot.

Why is the water hot when the tado app hot water setting is set to off for four days and the immersion heater is switched to off? I am attaching pictures of the system.

I am concerned because this means I cannot turn off the hot water and so may be getting very high bills.

Any ideas appreciated. Thank you.