The free diy home improvement guide with answers to your questions on a wide range of do it yourself projects.


Heating and Hot Water Valves

Several types of valve are used in the control of central heating and hot water in the home.  Valves basically control the flow of water along a pipe or close it off all together.

Motorised Valves

These have two parts to them – the head and the body.  The motor and a spring are housed in the head whilst the body contains the valve itself which directs or restricts the flow of water.  When the synchronous motor on these valves is energised it moves the valve to one position.  When de-energised, a spring pulls the valve back to the rest position.

Two Port Motorised Valve

As the name would suggest, this valve has two pipe connections.  They are positioned on a pipe run allowing the flow of water to be opened or closed.  Common applications are where central heating systems are zoned.  In this situation you may have the heating on in one area of the house and off in another.  The two port motorised valve is closed to stop the flow of water to the circuit where heating is not required.  In its resting state the valve is closed and when the motor is energised it opens

Three Port Motorised Valve

These are used to control the flow of water from the boiler to the central heating circuit as well as the hot water system and come in two types – the diverter valve and the mid position valve.  They both have three pipe connections but they have different capability.  The flow comes in at the central port and out at the other two

Diverter Valve

This valve can allow flow of water to either port A or port B but not both.  When the valve is energised, the motor opens port A and when de energised, the spring pulls it back leaving port B open.  In general, port B is used for the hot water circuit.

Mid Position Valve

Unlike the Diverter Valve, the mid position valve can allow flow to port A and port B at the same time.  So, in the mid position, both the central heating circuit and the hot water circuit will be active. As with the diverter type, energising the valve opens port A and de-energising returns it to its resting position – port B open.  Mid Position Valves have an override lever which can be used if necessary to move the valve manually to the mid position

Bypass Valve

These are designed to overcome potential problems on systems where thermostatic radiator valves or two port zone valves have been installed.  If all the TRVs on the system are closed at the same time or zone valves close, an automatic bypass valve will allow some water to continue to flow round the circuit.  Without this, the pump may be trying to push water round a system that is closed and this will cause unnecessary wear and increased noise levels.  The bypass valve will open as the pressure in the system reaches a certain level so that the circuits are never completely closed. The pressure at which it opens is adjustable.

Radiator Valves

Manual Radiator Valve

Manual radiator valves are used to control heat output from the radiator.  The cap on these valves can be turned to open and close the valve manually to increase or decrease the flow of water.

Lockshield Valve

lockshield radiator valveThis type of valve is fitted to the radiator to allow the water flow to be restricted in order to balance the system.  The cap on this does not turn and must be removed to allow the valve to be adjusted using a wrench.   Once they have been adjusted and the system balanced they are left alone.  Without these, water to the radiators nearest the boiler would get more than their fair share and the farthest ones may not get enough.  Balancing the system will allow all the radiators to heat up at the same rate.

Thermostatic Radiator Valve

thermostatic radiator valveThese valves are a big improvement on the manual radiator valve as they can control the flow of water to a radiator according to the temperature around it.  The advantage is that flow of water to the radiator will be gradually restricted as the room temperature rises and closed off when it reaches the required level.  As the room cools, the valve will gradually open again.  A thermostat is mounted in the head and this operates a spring loaded pin to control the valve.  As the temperature increases, the pin is forced down to close off the flow.  As it cools, the spring returns it to its resting position with the valve open.  Unless a bypass valve is fitted to the circuit, you should not fit a TRV to every radiator.  The flow to at least one radiator must remain open so that water can continue to flow around the rest of the pipe work if all TRVs are closed.

Some thermostatic radiator valves are designed in such a way that they must be fitted to suit the flow.  Fitting them the wrong way round will lead to water hammer.  Others may be fitted either way round and some are switchable
T&S Heating Limited