What each does
A programmable timer turns heating on and off at set times. A smart thermostat learns your schedule, adjusts automatically when you're out, and can be controlled remotely via app.
Energy savings
Standard programmable timer: saves energy vs no controls, but relies on you programming it accurately. Smart thermostat: Energy Saving Trust estimates additional savings of £75–£150/year vs a programmable timer through intelligent scheduling and geofencing.
Payback period
Smart thermostat fitted: from £189. Annual saving: £100. Payback: under 2 years — then saving every year after.
Convenience
Control your heating from anywhere in the world. Extend the heating if you're running late. Turn it off if you forgot when you left. The quality of life improvement is significant for most users.
Verdict
The smart thermostat wins on every measurable metric. The only reason not to upgrade is if your boiler isn't compatible (rare in post-2000 boilers) or if the upfront cost is a genuine barrier.