Which smart thermostat fits your boiler?

A smart thermostat helps you save energy without sacrificing comfort. But not every smart thermostat works with every boiler/heating system. In this guide you’ll learn what fits your setup, whether you need OpenTherm, and what to check during installation.

Last updated: 22-02-2026Smart Home

In 30 seconds: how to pick the right smart thermostat

Choose control type: OpenTherm (modulating) or On/Off.
Check your system: modern high-efficiency boiler → often OpenTherm. Older boiler → often On/Off.
Pick your ecosystem: app + schedules, optional Google/Alexa (model-dependent).
Want per-room heating? Add smart radiator thermostats.

View smart thermostats ›View radiator thermostats ›

Why compatibility with your boiler matters

A smart thermostat communicates with your heating system. If that “language” doesn’t match, you get less comfort or lose features like modulation.

✕ Temperature swings
✕ Unnecessary energy use
✕ No modulation (boiler runs harder than needed)

Which types of boilers/heating systems exist?

Combi boiler (most common)

Heating + hot water. Usually compatible if you choose the right control type.

High-efficiency boiler (HR)

Most efficient with OpenTherm/modulating: stable comfort and often lower usage.

Hybrid system & heat pump

Compatibility is extra important. Not every thermostat supports hybrid/heat-pump control.

OpenTherm vs On/Off: what’s the difference?

Control type	Benefits	Best for
OpenTherm (modulating)	More stable comfort, better efficiency, boiler modulates smoothly	High-efficiency boilers, modern installs
On/Off	Simple, broadly compatible, often easy to install	Older boilers, simple wiring

Practical advice: if you have a modern high-efficiency boiler, OpenTherm is usually best. For older boilers, On/Off is often the safe choice.

Quick decision tree

Do you have a modern high-efficiency boiler?

Yes → preferably OpenTherm. No/older boiler → consider On/Off.

Do you want per-room heating?

Smart radiator thermostats enable zoning (comfort + savings).

How do you want to control it?

Schedules, geofencing and optional voice (Google/Alexa).

Recommended smart thermostats (for your boiler type)

View all smart thermostats ›

Tip: first choose your control type (OpenTherm or On/Off). Then pick the right thermostat.

Frequently asked questions

How do I know if my boiler supports OpenTherm?

Check your boiler manual or the data plate (look for “OpenTherm”, “OT” or “modulating control”). If you’re unsure, check the terminals (often OT/RT) or ask your installer. Many modern high-efficiency boilers support OpenTherm.

Does every smart thermostat work with every boiler?

No. It depends on the control type (OpenTherm vs On/Off), your existing thermostat wiring, and sometimes the brand/protocol. If you choose the wrong type, you may lose modulation features or get unstable temperature control.

Which is better: OpenTherm (modulating) or On/Off?

OpenTherm is usually better for modern high-efficiency boilers: more stable comfort and often lower usage because the boiler modulates smoothly. On/Off is simpler and broadly compatible, especially for older systems.

Do I need smart radiator thermostats in addition to a smart thermostat?

Not required, but ideal for per-room heating. Radiator thermostats let you heat living areas more and bedrooms less — improving comfort and potentially saving energy.

Can I install it myself?

Sometimes (for simple 2-wire On/Off setups). For OpenTherm, hybrid systems, heat pump integration or any wiring uncertainty, use an installer.