Thermostat what and where?

Garage converted into flat and independent pump on thermostat in kitchen, will only be used for storage so heating will be at lowest setting, just to stop freezing.

So rest of house, lower floor living room which also has open fire, kitchen, and dinning room, plus shower and toilet.

Top floor two bedrooms plus bathroom, office (bedroom 2), and craft room (bedroom 1).

So three main rooms are living room, office and craft room, these will have wifi TRV heads, likely the two bed rooms with have terrier i30 heads so they are only heated at night and will not over heat. Also likely dinning room and kitchen will have terrier i30 so they are not heated at night.

But don't want boiler running 24/7, I want it to auto shut down when not required, so some where I need a thermostat, it would seem most likely place is in the hall which has stairs to landing, the hall radiator is between snug (dinning room) and front door, the latter rarely used, so if thermostat put in hall, either opposite radiator on cupboard under stairs wall which is rather close to radiator, but ticks boxes reading the thermostat instructions, or short wall between hall and utility room. There are marks on wall which suggest it was on very short wall hall to kitchen on hall side.

Landing has no radiator but will clearly be heated from hall radiator that is other option I think?

So seems three options, opposite radiator in hall, on hall side of kitchen to hall wall, or landing, which would be best?

Next is type of thermostat, since central heating also heats water, although at moment no control over water heating, Nest 3 seems to tick the boxes, however that would need a motorised valve adding to control hot water and a thermostat on the hot water tank, and then finding a way to get wires between them all.

Or could have simple Nest e which would simply switch off boiler once house warm. But work clearly needs doing, need non return or check valves adding as at moment if pump not activated then water flows in reverse warming radiators slightly when set to domestic hot water.

There is a programmer, however it does not seem to matter where set, even set to hot water only twice a day, radiators still get hot. There seems to be no direct connection between pumps and programmer.

So as it stands, programmer turns on boiler and domestic hot water is heated, if thermostat in converted garage is set high enough one pump will circulate water around the converted garage. The other pump has a 13A plug on it, and if plugged in, then main house gets circulated hot water to radiators. As a temporary measure I have a smart socket supplying that pump so I can switch main house heating on/off.

Clearly it needs modifying, my knee jerk reaction is fit a Nest e to control second pump, but pumps don't have micro switches, so how do I power boiler at same time as pump. I can add a relay box of course, but would like to use a standard system.

Best option is trial and error.put the thermostat in one location and see how it performs. Although hallway may be the usual place it doesnt mean it works for everyone. Sometimes a stat located in one position caused the heating to go off too soon before the rooms hit the desired temp, leaving you with cold rooms.

In other locations the area around the stat may not get warm enough to switch off even though other parts of the house may be baking hot.

Try it in different areas of the house and see which works best tor you. Usual locations will be hallway upstairs or down, or on wall on the stairs themselves. Some homes it will be in the living room.

With the gas modulating boiler the wall thermostat was really there to stop boiler cycling once all rooms warm, but the oil fired boiler may be classed as modulating but 18 to 25 kW is rather pointless, it basic turns on/off not up/down so a room thermostat could be the main control.

I tried the idea of setting the TRV to stop over heating and moving the thermostat to room in use. Used a Horstmann HRFS1 it was a failure, it would fail to turn off or fail to turn on too many times, it was only when it failed I realised why people pay the extra for a Honeywell Y6630D which is not programmable may be double the price but it has a fail safe.

I would prefer hard wired, but getting the wires through floors is not easy, so may be forced to use wireless.