Radiator Valve Installation

A typical radiator has two valves. On the flow side sits the control valve, which you use to set the temperature. On the return side sits the lockshield valve, which lets the radiator be isolated and sets how much water passes through it.

• Thermostatic radiator valve (TRV) with a head: it reduces the flow on its own according to the room temperature, and it is now the standard choice in flats and houses
• Manual valve: you open and close it by turning the handle, which suits utility rooms or spaces where the temperature hardly changes
• Valve with presetting: it limits the maximum flow through one radiator, which matters when the system is balanced
• Angled or straight pattern: chosen according to whether the pipe comes out of the wall or up from the floor
• Bottom-connection radiators: they have a built-in valve insert, and a connection fitting is installed underneath the radiator

The valve body is usually brass, often nickel-plated. Plastic is mostly used for heads and caps. When choosing, make sure the valve fits the existing pipework and that a suitable thermostatic head is available for it.

Not every heating problem means a new radiator. Often a new valve is enough. Think about replacing it when:

• There is damp, limescale or rust staining around or below the valve
• The radiator stays fully hot even with the head turned to minimum
• The radiator stays cold while the others heat up
• The valve hisses, whistles or knocks
• The pin under the head is stuck and will not free up

It pays to combine the valve change with other work: new radiators, decorating, new flooring or insulation. After a block of flats has been insulated, the whole building is often rebalanced, and the valves in all flats are then replaced at the same time.

Isolating and draining

A valve body cannot be changed under pressure. In a house, the heating engineer switches off the boiler, lets the water cool and drains at least the part of the system being worked on. In a block of flats with central heating, the riser has to be shut off and drained. This must be approved and arranged by the building management or owners' association, so the date is agreed in advance.

Removing the old valve

The old valve is undone with a spanner while the pipe is held so it does not twist. Threads and seating surfaces are cleaned. If a thread is damaged or corroded, it has to be repaired, otherwise the new joint will not seal.

Fitting the new valve

Threaded joints are sealed with hemp and jointing paste or with sealing tape rated for heating systems. Some valves come with a built-in seal. On copper pipe, compression fittings with a new olive are common. The valve is fitted according to the flow arrow and tightened firmly but carefully, so the nut or the radiator tail does not crack.

Refilling, bleeding and testing

The system is refilled, every radiator is bled and the pressure is checked. With a boiler in the house, the pressure is topped up to the value given by the boiler manufacturer. If the system was drained, a corrosion inhibitor is usually added again. The joints are then left under pressure and checked once more when the water is hot.

Head and settings

The thermostatic head goes on last, usually set to fully open. If the valve has presetting, it is set according to the balancing calculation or the heating engineer's recommendation.

The simplest case is a house where the radiator is easy to reach, the pipework is sound and the new valve has the same dimensions as the old one. Then it is a straight swap.

These things make the job longer and more costly:

• A radiator in a narrow recess, behind furniture or behind tiling
• Old steel pipework that cracks when loosened or has rusted threads
• A different spacing or connection type, so the pipework needs adjusting
• Having to shut off a riser in a block of flats and wait for a date from the management
• Working during the heating season, when the system has to be drained and restarted
• Many radiators that need balancing afterwards

On the other hand, replacing valves in several rooms at once usually makes each valve more efficient to do, because draining and refilling happen only once.

• Poorly sealed thread: too little sealant or the wrong kind, and the joint starts to drip after a while
• Valve fitted against the arrow: it then hums or knocks, and the thermostatic control does not work properly
• Overtightening: it damages the nut or the radiator thread
• Skipped bleeding: the top of the radiator stays cold and the system gurgles
• Ignored balancing: radiators near the boiler get too hot and those further away never warm up
• Badly placed head: for example covered by a curtain or pointing up over a hot pipe, so the sensor reads a different temperature from the room

If your building has heat cost allocators on the radiators, tell the management about the replacement, so the billing is not affected and the valve settings match the other flats.

Leave replacing the valve body to a heating engineer, especially in a block of flats. You can, however, safely change the thermostatic head yourself, as it fits onto the valve without draining any water, and bleed the radiator afterwards.

1. Identify the valve type and connection, and if needed buy a head with an adapter that matches the valve manufacturer.
2. Turn the old head to its highest setting.
3. Loosen the nut or locking ring and pull the head off.
4. Check that the valve pin springs back after you press it, and if it is stuck, gently free it.
5. Set the new head to its highest setting, fit it and tighten it by hand.
6. Place a cloth and a small container under the bleed valve.
7. Open the bleed valve with a radiator key and leave it open until water runs without bubbles.
8. Close the bleed valve and, if you have your own boiler, check the pressure gauge.
9. Set the head to the level you want and check after a few hours that the radiator heats evenly.

At handover, go through these points with the heating engineer:

• Joints stay dry with hot water and after several hours of running
• The valve is fitted according to the flow arrow
• The radiator heats across its whole surface, with no cold top section
• The head responds, and the radiator gradually cools when it is turned to minimum
• The head is not covered and faces into the room, not upwards
• The valve presettings are written down and you know what values are set
• The system pressure matches the boiler manufacturer's figure
• The area around the radiator is clean with no water marks
• In a block of flats, the riser has been refilled and the management knows the work is finished