Thermostat temperature keeps changing and is never same as I want it per schedule

[dgovan]

I have read everything I can but I am baffled by what my Nest learning thermostat has started doing.  For years we have run happily on using a manual schedule setting different temperature and times for different days.  But now we are getting a "time to temperature" reading coming up.  The temperature shown is never the same as what is manually scheduled and even when we adjust it to be the same it reverts after a while to its own temperature.  Is this something new that has recently been added?  How do we switch it off?  We were happy with our manual schedule but now it seems to be being overridden.

(Sorry but I have no idea which generation of nest learning thermostat we have,)

[Eureka]

The time to temperature shows how long Google calculates it will take to reach the desired temp. It does this when the temperature is changed manually or through the app. My guess is that there's some auto routine in your Google home app that keeps being triggered and it is overriding your manual settings. If the boiler has another controller such as a third party app or remote, check the temp set on these too.

[dgovan]

Very many thanks.  Yes in my Home app there was a "good morning" action which included setting thermostat.  It wasn't ticked and didn't have a set temperature but I have deleted that and I'll see what happens.  I didn't even know these routines were in the Home app - must have been introduced recently.