A thermostatic radiator valve measures the room temperature and adjusts the flow accordingly. It does this by means of a sensor in the centre of the handle. As the room temperature rises expansion causes a rod to push down on the valve mechanism restricting the inlet flow of hot water.
The desired temperature is set by turning the handle. At the outlet (return) end of the radiator is attached the lockshield valve. This is adjusted by the plumber to balance flow rates through the system, ensuring all radiators get an adequate share of the available hot water.
Thermostatic radiator valves are recommended by plumbers and the government as energy saving. They are, if the temperature is set and maintained. In practice people may think it’s a little chilly then turn the valve full on. Left fully open they will save no energy at all.
The term thermoregulating valve is also used to mean thermostatic radiator valve. Strictly speaking a thermoregulating valve has both hot and cold supplies, such as on a shower, but more and more the term has come to have both meanings.
Manual radiator valves have no thermostatic control. The maximum flow of hot water out of the radiator is controlled by adjusting the lockshield valve on the radiator outlet as for thermostatic valves. The inlet valve with manual handle is used to turn the radiator on and off.
All valves supplied by Castrads are bi-directional. However under high flow conditions a bi-directional TRV valve can vibrate if it is on the return and not the conventional flow side of the radiator. For this reason it’s best to install the TRV valve on the flow side and the lockshield on the return side of the radiator.
High flows are likely on radiators near the boiler. On these radiators flow should be reduced by means of the lockshield valve. As well as eliminating vibration this also serves to balance the system giving similar flow rates in radiators close or far from the boiler.
How can I tell which is the flow side of my radiator?
Close the lockshield valve then reopen it a fraction. After half an hour at restricted flow you will find one pipe much warmer than the other. The warmer pipe is the flow pipe.
i. Screw the valve tail into the bottom of the radiator, using a sealant such as PTFE tape or LSX sealant, available to buy here. Be sure not to overtighten the valve tail as this can crack the bushes.
ii. Slide the valve body over your copper pipe, ensuring the olive (little brass ring) is inside the valve. When the bottom nut is tightened, the olive is compressed, forming a watertight seal around the copper pipe.
iii. Connect the valve body to the valve tails by tightening the large nut located on the end of the tail onto the threaded end of the valve body.
