A Guide to Thermostatic Radiator Valves (TRVs)

Someone putting money into a pink piggy bank sat on top of a radiator
2 October 2023 5164 view(s) 5 min read
A Guide to Thermostatic Radiator Valves (TRVs)

What Is a Valve?

A valve is a simple tap that regulates the flow of hot water in and out of the radiator which then changes the temperature of the room. There are two types of valves: non-thermostatic (manual) and thermostatic (TRV). The TRV controls the radiator's temperature by sensing the room air temperature and automatically opening and closing the flow to the radiator to maintain a pre-set temperature. A manual valve maintains the temperature of the radiator regardless of how warm the room is. TRVs are now a requirement as part of Building regulations, check with your installer to make sure you have the correct valves. The thermostatic valves can be installed on all radiators, without any special adaptations.

In a radiator, there are two types of valves the wheelhead for the water inlet (also known as the flow) and the lockshield for the outlet (return). The wheelhead valve is the temperature control; the lockshield valve is used to balance the radiators in the system so that they all heat up at roughly the same rate. Simply put, the radiator closest to the boiler if left unchecked would heat quicker than the one sited at the other end of the house, so the lockshield valves should be set opened at increasing amounts the further away from the boiler the radiator is.

The thermostatic head, if any, works best if mounted on the flow/inlet side of the radiator.



What is a Thermostatic Head?

The thermostatic head is a device installed on a radiator that allows you to automatically regulate the flow of hot water into that radiator. The head will increase or decrease the flow of hot water to the radiator depending on the ambient room temperature. This allows you to set the valve to stay open until the temperature you want to reach is achieved. If the temperature then drops the valve will reopen.

The main element of the thermostatic head is the control "motor" containing a specific thermostatic liquid. The liquid will expand or contract depending on the room temperature. If the temperature in the room is higher than the pre-set one (e.g. 20°C) on the valve, the thermostatic liquid will increase in volume causing the actuator (cylindrical body similar to a plug) to move, closing the valve which in turn reduces the flow of hot water into the radiator. If the ambient temperature is lower than the set temperature, the reverse process occurs, and the valve opens and the radiator will heat up.

A white thermostatic radiator valveA white thermostatic radiator valve


The Advantages of Thermostatic Heads

Thermostatic heads help to reduce waste and improve comfort by stabilizing the temperature in each room as required. Thermostatic valves are now a requirement as part of Building regulations, check with your installer to make sure you have the correct valves.

A topdown floor plan detailing optimum room temperatures in the homeA topdown floor plan detailing optimum room temperatures in the home

They are a very smart solution because they allow you to improve the level of energy consumption related to heating and consequently can provide a significant saving on the gas bill.


Correct Use of Thermostatic Heads

Keep the thermostatic head as free as possible, (the room temperature sensor must be able to detect the temperature inside the room). Remove anything that prevents normal air circulation near the radiator (curtains, furniture, radiator covers, shelves).

Remove any heat sources (such as ovens or stoves).

Close the valve when you have doors or windows open, keeping windows open and your heating system on at the same time wastes a lot of heat and money!

Leave the head fully open at position 5 during the summer period, so as to avoid the formation of limescale and the consequent blockage of the head.

Leave the valve on 1/2 in rooms that are not in use or if you leave the house empty for a few days.


How to Distinguish a Normal Valve From a Thermostatic Valve?

Most thermostatic radiator valves have numbers, graphics or other control buttons, manual valves usually have no numbers or buttons.

There may be signs such as plus and minus (or on/off) indicating the direction in which you need to turn it to open or close it.

To understand if a valve is manual or thermostatic, simply unscrew the valve knob, if it has a piston that can be pushed in, then you can be sure that the valve is thermostatic. Replacing a manual valve with a thermostatic head will allow you to adjust the room temperature in order to ensure better comfort, and energy saving and reduce CO2 emissions.


Certification of Thermostatic Heads

To ensure optimum operating performance and to avoid unnecessary costs and degradation, certified thermostatic valves meet the following specifications (proven by the KEYMARK certification scheme):

  • Opening and closing characteristic curve
  • Flow rate at different pressure differences
  • The influence of water temperature
  • The closing speed
  • Temperature resistance
  • Mechanical fatigue test
  • Thermal fatigue tests
Previous article:
Next article: