Buying guide
OpenTherm explained for UK boiler owners
GuideDraft for owner review — wording and facts to be checked against sources before launch.
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The short answer
OpenTherm is a way for a thermostat to talk to a boiler. Instead of simply switching the boiler on and off (called relay control), an OpenTherm thermostat can ask the boiler to run at a lower or higher output. Boilers that run gently for longer tend to work more efficiently than ones that keep starting and stopping.
How do I know if my boiler supports it?
- Look in your boiler’s manual or on the manufacturer’s website for “OpenTherm” or “OT”.
- Some boilers have two small low-voltage terminals marked for OpenTherm.
- If you can’t find it, assume relay control. Every smart thermostat in our list also supports relay control.
Which thermostats in our list support OpenTherm?
| Product | OpenTherm | Notes from the manufacturer |
|---|---|---|
| tado° Smart Thermostat X Starter Kit | Yes | Relay or OpenTherm; also listed for heat pumps |
| Hive Thermostat Mini | Yes | Compatible combi boilers only; single zone only |
| Hive Thermostat | Yes | Compatible combi boilers only |
| Wiser 1 Channel Smart Room Thermostat Kit (2nd Gen) | Yes | Relay and OpenTherm; combi boilers |
| Wiser 2 Channel Smart Room Thermostat Kit (2nd Gen) | Not listed | Relay connection listed; for boilers with a hot water cylinder |
| tado° Wired Smart Thermostat X (2nd gen) | Yes | Relay or OpenTherm; replaces a wired thermostat |
| Netatmo Smart Modulating Thermostat | Yes — required | Works only with OpenTherm modulating boilers |
| Netatmo Smart Thermostat | Not mentioned | On/off (dry contact) control |
Does OpenTherm save money?
It can help a boiler run more efficiently, but how much depends on your boiler and your home. Hive, for example, claims up to 12% extra savings with OpenTherm on compatible combi boilers — that is the manufacturer’s claim, not a figure we have measured. Use our savings calculator to see what different reductions would mean for your bill.
Before you buy
Check your exact boiler model against the thermostat maker’s compatibility list, or use our boiler compatibility checker.
Our picks
tado° Wireless Smart Thermostat X Starter Kit (with Hot Water Control and OpenTherm)
Best for: Homes that may later add room-by-room control, including heat-pump homes.
Netatmo Smart Modulating Thermostat
Best for: Owners of an OpenTherm boiler who want modulating control and fault alerts.
Wiser by Drayton 1 Channel Smart Room Thermostat Kit (2nd Generation)
Best for: Combi-boiler owners who never want a subscription and may add radiator thermostats later.
Hive Thermostat Mini
Best for: Combi-boiler homes that want a low-cost smart thermostat.