Learning thermostats and boiler problems?

I hope my boiler is now fixed, however so many times before I have thought fixed but then found it has still locked out, however it is not the fixing of the boiler, but the Nest Gen 3 learning thermostat I am asking question about.

The thermostat can have no way to know the boiler has failed, I have looked at the orange temperature display, realised can't hear boiler running, felt radiator, and if cold gone down to reset, but the thermostat must be recording a long time to heat the house.

The TRV must be the same, it will start opening more and more waiting for the room to warm up, and when boiler finally is reset, the radiators get really hot before the TRV head has time to close the valve.

I have put off the setting of lock shield valves as never sure if room cool due to boiler failure or poor settings.

So looking at the schedule I have this.
It seems it has altered all on it's own. I set 5 changes per day, the 0.5°C changes are set as radiator a far distance from thermostat and so it tends to over shoot, over heating is a problem as the hall is slowest room in house to cool, and that is where the fixed wiring is for the thermostat, since the heat link is in the floor below, not normally heated, relying on wireless linking is not really a good idea, so hard wiring between heat link and thermostat.

I will alter and remove the schedule now, but this changing without my knowing seems rather odd.

Sorry cant help but 18, 19 and 20c would be freezing for me.

If this happened recently, our nests started offering to recalculate the schedule for efficiency last night and showed a gold colour cog on the display. We declined it so no idea what it does.

The 18 to 19 setting is to ensure the boiler runs, that is setting in the hall, the living room TRV heads are set higher.

Lower said:

If this happened recently, our nests started offering to recalculate the schedule for efficiency last night and showed a gold colour cog on the display. We declined it so no idea what it does.

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Mine did the same, but after correcting the schedule it has not altered again. In warmer weather we set the DHW to 5 days a week ½ hour each day it runs, but turn it off in winter, water gets hot enough without it, being a C Plan.