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A central heating valve that is difficult to maneuver or leaking through the shaft must be replaced. Take advantage of this intervention to equip the radiator with a thermostatic valve that is better able to regulate the temperature.

Put a thermostat on a radiator

Practical advice

The ease with which you can replace a regular faucet with a thermostatic can make you change all those in your facility. You will gain in comfort as each room has its own temperature control system.

A thermostatic faucet

The substitution of the radiator valve is facilitated by the fact that both models are bent type. They have substantially the same size and the same mode of connection in 15/21. A thermostatic faucet consists of two parts: a T-shaped body and a temperature adjustment head which is clipped onto it

How it works?

With the 15/21 female inlet, one of the three branches of the T is intended to be connected to the hot water supply pipe. The 2nd branch is joined to the radiator by a conical bearing connection. The third branch is equipped with a needle device that manages the flow of water controlled by the head. It looks like a big graduated button to preset the trigger. The active element that acts on the needle is a bulb of wax that liquefies or solidifies as a function of temperature. The positioning of the needle conditions the flow of water in the radiator and therefore the temperature of the room.

Drain before dismantling

Before any modification of the installation, it is necessary to drain at least the top of the radiator concerned. Reduce the amount of water in the installation at the boiler.

● Disassembly of the original faucet is easily accomplished by unscrewing the bushing which joins the two parts of the conical fitting mounted on the radiator. Next, unscrew the fitting that connects the valve body to the supply piping.
● The thermostatic valve is sold in two parts: the head on one side, on the other the body with its conical seat fitting which will replace the one that fitted the radiator. Disassembly / reassembly requires a special 14 mm hex key: it engages inside the fitting. The sealing of the joints with the radiator as well as the connection to the supply piping is provided by the bead associated with joint compound.

Keep the initial setting button

A button is provided with the T: it allows to open the tap fully before the head comes to cap the needle. Fixing is done by clipping. A simple pressure at the end of the head is enough.
● The temporary adjustment button is to be retained. In case of anomaly of the head, it can troubleshoot by turning the thermostatic into a normal faucet. Nevertheless, the head can be changed by unlocking a ring located at its base.
● After filling the system with water and heating, the purge of each radiator is necessary to eliminate any air pockets that may have formed.

Thermostatic valve

Thermostatic valve

The thermostatic valve (Danfoss) is packaged in two boxes. On the left, the T with its tapered seat (A) and the needle device (B). Right, the head clipping on it.

Unscrew the tap

Unscrew the tap

The conventional faucet is removed by unscrewing the radiator nut bushing. At the rear, turn the valve to unscrew it from the elbow fitting that terminates the hot water supply line.

Remove the coupling

Remove the coupling

To disassemble an old cone seat fitting, insert a square section iron into the hole in the fitting. Hold the iron and unscrew with a wrench or flat wrench.

Coat threading

Coat threading

Coat the thread of the new fitting with solder paste and roll up the tow. Screw the fitting in by hand and lock it with a hexagon key of 14.

Seal

Seal

Seal the body of the thermostatic valve (tow + sealant). Then screw the body onto the elbow fitting of the hose. One wrench (A) holds the fitting, the other (B) screws the body.

To screw

To screw

Screw the nut of the radiator fitting onto the body of the thermostatic valve. By hand then with a key. Sealing is achieved by the conical parts of both parts.

Initialize the needle

Initialize the needle

The provided temporary button snaps onto the body. Turned fully, it allows to initialize the needle in the maximum open position.

snap

snap

Place the maximum aperture mark of the button in front of the green index of the fixed ring. Position the head on the body. Then push: the snap is on the ring.

Are thermostatic faucets still relevant?

Are thermostatic valves on radiators still relevant? Are there more modern ways to program the heating?
Christian Pessey's answer:
Thermostatic valves are not made a priori to "program the heating". They regulate the radiators piece by piece. Conventional models operate mechanically, a valve opening or cutting off the power supply of the radiator. But we see appear thermostatic taps connected, programmable, can be remote controlled from a smartphone, a computer, a tablet... via a box. Thermostatic valves are not yet exceeded...


Video Instruction: Thermostatic Radiator Valves - Plumbing Tips