How to install a thermostatic radiator valve

In a traditional gas central heating system, a room thermostat is set up in a frequently used room and used to switch the boiler on when the room temperature drops below the set temperature. The boiler then sets about heating up the water before a circulating pump sends it towards all the central heating radiators in the system until a set temperature is reached in the home. However, some rooms in the home gather more heat than others – for example, a south-facing room with French windows – and do so independently of the heating system. A sunny room therefore requires less heat than one with no sun exposure and a thermostatic valve can be used to adjust the heating system accordingly.

Steps

1. Turn off the water and drain the radiator

2. Install the TRV tail

3. Install the TRV

4. Position the TRV and turn the radiator back on

Before starting installation, it is imperative to:

• turn off the water supply;

• drain the radiator.

If you do not drain the radiator before removing the existing valves, you will have a lot of water on your hands. What's more, you'll be dealing with grimy water that has spent a long time in the radiator.

The valve tail should be screwed directly into one of the four valve points in the radiator. This part is unusual in that it does not always feature a flat outer surface for a traditional tool to get purchase on. You will therefore usually have to use a radiator key to tighten the valve tail.

This key is usually inserted into the tail piece which can feature a square or hex socket. If the tail comes with a black rubber ring, this is a seal. Simply put the seal in place and tighten the nut until it compresses the seal and creates a watertight seal. If a rubber seal has not been provided, you should use PTFE tape or pipe sealing cord.

• TRVs can be straight or angled (90 degrees). Choose the option that best suits your installation according on the position of your pipes.

• The rad valve will have one male end and one female end. The male thread should be connected to the tail piece in the radiator and the female thread should be connected to the hot water feed.

• The hot water feed should feature a male thread and must be wrapped with PTFE tape before the TRV is screwed into place. Be careful to ensure that the head of the TRV is in the correct position as you finish tightening. A properly vertical or horizontal rad valve will be more attractive than one at an angle!

• Tighten the nut onto the male end of the TRV using water pump pliers. There should be no seal in this connection. This part uses a compression fitting in which the metal parts are compressed to create a watertight seal.

To fit the head of the TRV to the rest of the valve, unscrew the head as far as possible (setting the temperature to minimum) and position it on the valve. A metal securing ring is used to connect the two parts and should be screwed into place by hand. Once this nut is tightened, your TRV has been installed.

All that's left to do is to connect the radiator to the water supply, bleed the radiator and check for leaks around connections.

In a central heating system with a classic circulating pump, it is important to keep one radiator without a TRV and to never close this valve entirely. Why? Well, imagine that all your TRVs are closed at the same time but the thermostat has not reached the set temperature. The boiler will keep running, the pump will push out water but to no avail because all the valves are closed. This is not good for your heating system! It is therefore essential to fit one of your radiators with a traditional valve and to keep it partially open at all times to keep the water flowing at a minimal rate in the system. Modern valves come with a little flange that prevents the valve from being closed entirely. It is found beneath the protective cover that is fitted over the head of the valve.

This precaution applies to systems with a classic circulating pump. Modern systems fitted with circulating pumps with variable speed technology are designed to adjust the flow of heated water automatically to account for this phenomenon. Another solution is to install a differential bypass valve. However, this option is best used for heating systems in large buildings.

Required skills

You need a few basic plumbing skills to install a thermostatic radiator valve. You will usually have to be able to apply PTFE tape, know how to connect various parts and fit a compression fitting.

Time required

10 to 30 minutes

Number of people required

1 person

Tools and equipment

• Thermostatic radiator valve

• Radiator key

• Adjustable spanner

• Water pump pliers

• A set of screwdrivers

• Pipe sealing cord

• Paste sealant

• Cloths

Safety and workwear

• Workwear

• Protective gloves

• Safety goggles

This list is non-exhaustive. Be sure to match your safety and workwear to the task at hand.