Got up at 03:00 to make a cuppa and heard water running
Hadn't quite closed the service valve under the sink. Sigh of relief.
I have several thermometers dotted about. On in the services cupboard where I read the meters. It is always at leas three degrees in there, more usually six when it is below zero outside (I drop a probe out of a window). I would drill a hole for the probe if it wasn't so cold outside.
I have an inside/outside one in my room but the outside is unreliable as the probe is shoved through a (closed) vent, but I suspect that heat from the room bleeds through and skews the readings.
A pain to relocate on PVCu windows.
Since I took that photo, five minutes ago, it has dropped to 2.3°
Actually -1.5°C that side of the house (north facing) but 4°C at the front (direct sunlight).