"Smart" thermoststat - logs ?

That's Tuya stuff, I think? Do you have any 'hub', or is it just a wifi thermostat directly on their cloud?

The wifi thermostats are quite basic (often an ESP8266 or similar) so I doubt it keeps much in the way of logs since it doesn't have persist storage beyond its own program flash. The cloud account thingy might log something, but I doubt the thermostat phones home to the cloud every time it decides to turn the heating on.

IoT stuff is not known for its reliability...

Theo

Do you have stored hot water? If so when is that set to re-charge?

That plus a stuck zone valve could cause unexpected CH running.

(also CH system still on BST could leave it running later than expected)

No, it's a combi boiler. And time seemed to update automatically (presumably from network ?)

You have a boiler that is connectd to a network!

Some combis have a small heat store to ensure hot water is quickly available. It can fire to heat this water at any time.

Most combis will have one or more valves, any one of them might not be seating properly, perhaps some crud holding a valve open.

Surely, if you are up regularly at 3AM, you want the heating on then?

In any case, how much does it really save to let the place cool down overnight, then have to reheat it in the morning?

Sure, the heat loss is lower overnight than if the place were at full temperature then, but is the saving significant?

More likely just from a memory chip in its own clock timer. Most modern timers know the date and when BST starts/stops.

You could buy a Temperature Data logger* (about £20) that plugs in to a USB port on your computer to set it up (sampling frequency etc), remove it, tape/tie it to a CH pipe/rad, let it run for a few hours/days/weeks, plug back in to PC and download all the readings. That will tell you what's going on (but not why, of course). I have a couple I used for settings things up, worls well.

If that also heats a rad, I'd look for a better installer.

Or a better boiler, rather than one that allows debris to keep an internal valve partially open and leak into the radiator circuit.

This obviously passed you by.

We have a number of Tuya devices - although our heating is Hive based. I?ve noticed the very occasional ?phantom? device turn on. Ours are things like lights, electric blankets etc. The phantom turn ons are raw, one every few months if that, across perhaps 10 devices.

I?ve not noticed this with the Hive system.

Another thought, where is the boiler and does it have a frost stat? Our boiler is in the garage and, if it was cold, it could fire up if the frost stat was tripped. I don?t recall it happening but that doesn?t mean it hasn?t.

Most take the advice of their installer as to what boiler to buy.

Hence finding a better installer.

My Ideal Logic has that, but it kicks in rather too frequently, and the clatter of the thing firing up and then purging etc once it's fired for 10 seconds or so makes it too intrusive - the entire cycle last about 5 minutes every hour or two.

The slightly odd thing to me is that there's no hot water store, beyond whatever's in the pipes and HX.

Vaillant eBUS ?

While ebus is a network of sorts, its not directly connectable to a TCP/IP lan. (it's a two wire 2400 bps serial bus running over a power feed)

A common fallacy. The downside is the discomfort factor if you get up before the temperature is restored. Just set the timer appropriately.

Only one channel, though.

For more fun build yourself an Arduino based logger. I strongly recommend using DS18B20 temperature sensors rather than thermistors. This is a single probe

Note that practically all DS18B20s on eBay are likely to be fake, and could give inaccurate readings and/or other issues.

I have one of the non-cloud based Heatmiser programmable stats, at one time I kept local logs from it, but I didn't keep it up ...