I’ve just moved house and the previous owner (very) recently fitted a new condensing boiler. The thing is, there’s no thermostat anywhere. All the radiators have TRVs on them with the exception of the towel radiators in the bathrooms and a tiny radiator in the old airing cupboard ( :?). There’s a mechanical timer on the front of the boiler which can be set in 15 minute intervals.

Silly question, if the heating is switched on all day (6am to 8pm currently), does this mean the boiler will be burning constantly? Or will the burner switch off if the water returning to the boiler is above a certain temperature (i.e. the TRVs have closed because the rooms are warm enough)?
The boiler also has a dial on the front, which I assume controls the water temperature.

Boiler should have a dial on the front to control the CH temperature. Adjust it with that.

Get a stat as soon as you can. Wireless ones run at about £100 for a decent one (Honeywell/Drayton) and shouldn’t be too hard to wire in. Quite surprised that if it’s a new boiler there is no thermostat as it’s part of building regs that all new installs should have one along with TRV’s.

The dial on the front controls the temperature the boiler raises the water to before it shuts off – essentially a high limit stat.

The towel radiator/airing cupboard radiator are heat sinks to allow the system to dump heat if all the valves are shut. It can be done this way or it can be done with a bypass valve.

The boiler will run until the high limit stat reaches temperature. Once it cools sufficiently it will run again.

A stat. will stop the boiler running once the location where it’s placed is up to temperature. It will probably be a bit more efficient as the heat sink rads will not be heated all the time but I would doubt massively so.

As northernmatt says, a stat is dead easy to fit but may require the boiler to be disassembled.

I’ve used altech stats from Graham’s the plumbers merchants which are cheaper than honeywell and work ok. Stats are a bit of a minefield as there’s wireless, wired, programmable etc.