Radiator thermostat with Shelly BLU TRV

When this is the right answer

An older house with water radiators and one thermostat for the whole floor. The customer wants rooms heated when they are used and not when they are empty, and does not want pipework opened up.

Shelly BLU TRV replaces the manual thermostat head on each radiator. Installation is a few minutes per radiator, it needs no wiring at all, and each head becomes its own zone with its own schedule.

It is a retrofit, not a rebuild. That is the whole appeal — and the reason it sells in buildings where underfloor heating never will.

A TRV brings its own thermostat with it. Where the heat is switched by a relay instead — an electric radiator, a convector, a towel rail — the app’s thermostat function does the same job with any Shelly relay and any Shelly temperature sensor; it is described under setting up a thermostat.

Check the valve first

This is the step that decides whether the job takes twenty minutes or ends with a second trip.

BLU TRV fits most radiator valves, but not directly — most need an adapter, and which adapter depends on the valve manufacturer. Danfoss alone has several incompatible thread standards across the decades.

Check the valve body against the valve compatibility list before you order, and bring the adapter with you. The marking is usually stamped on the valve body under the old head.

External sensors

The TRV measures temperature at the radiator, which is the warmest point in the room and behind furniture as often as not. Two additions fix the two problems that follow.

A room sensor for larger rooms

Pair a Shelly BLU H&T and the TRV controls on the room’s temperature rather than its own. In anything bigger than a bedroom this is the difference between a room that feels right and one that is always two degrees off.

A window sensor to stop wasted heat

Pair a Shelly BLU Door/Window and the TRV closes when a window opens. In a house where airing rooms is a daily habit, this is where the saving actually comes from — a radiator running full while the window is open is heat going straight outside.

Tips & best practices

Bring adapters to the first visit. The valve marking is under the old head, so you cannot check it from the doorway — and a return trip costs more than a box of adapters.
Do not fit one to every radiator. A room with two radiators needs two heads or none; one controlled and one open works against itself.
Balance the system afterwards. Adding zone control to an unbalanced system makes the imbalance more visible, not less.
Set back rather than switch off. A room allowed to fall to 15 °C costs more to recover than one held at 18 °C, and cold outside walls invite damp.
Batteries last a heating season, not forever. Note the fitting date, and change them all at once before the next winter rather than one at a time in January.

Video tutorial

Installation and pairing, from removing the old head to setting a schedule.

Loads YouTube when you press play. Watch on YouTube

By ShellyGuide on YouTube

This video is in Danish. Auto-translated subtitles are available in the YouTube player settings.