A thermostatic radiator valve (TRV) does a simple job, but it is a moving part that works every day for years. Over time it can stick, drift out of calibration or stop responding, and your heating quietly gets less efficient. The good news is that replacing a TRV is often a quick, cheap fix, and many people only need to replace the head, not the whole valve.
Short answer: replace a TRV if it is stuck, the room never reaches temperature or overheats, it leaks, or it is 10–15 years old. Often you only need a new head, which takes a few minutes and does not need draining the system.
Signs your TRV needs replacing
- The radiator stays cold when the heating is on and the TRV is turned up, but the rest of the radiators are fine. This is the classic sign of a stuck pin.
- The radiator is always hot, even when the TRV is set low and the room is warm. The valve is not closing.
- The room is too hot or too cold compared with the number you set, or the temperature swings up and down.
- The valve is slow to react, or the dial turns freely with no change.
- There is a leak or a damp patch around the spindle or the connection. Dried-up seals cannot always be fixed.
- Noise such as whistling or banging from the valve.
- It is simply old. TRVs commonly last 10–15 years. Older ones lose accuracy and respond more slowly.
Before you replace anything, rule out other causes. A radiator that is cold at the top needs bleeding (see what are airlocks?), and one that is cold at the bottom may have sludge (see does flushing radiators improve efficiency?). A closed lockshield valve on the other end also stops flow.
Try this first: free a stuck TRV pin
TRV pins often seize after being closed all summer. It is the most common TRV fault and it costs nothing to check.
- Turn the heating off and let the radiator cool.
- Unscrew the TRV head (the part with the numbers) by turning the collar anticlockwise. On some models it simply pulls off.
- Look at the small metal pin in the valve body. It should spring up when you let go.
- If it is stuck down, gently tap it or wiggle it with pliers until it moves freely.
- Refit the head, turn the heating on and check the radiator warms up.
If the pin is free and the radiator still will not warm up, or it will not close when it should, the head or valve needs replacing.
Replace the head or the whole valve?
A TRV has two parts: the valve body fixed to the pipe, and the head that contains the temperature sensor. Many faults are in the head.
| Part | When to replace | Difficulty |
|---|---|---|
| Head only | Slow, inaccurate or unresponsive, but the valve body does not leak and the pin moves freely | Easy. No draining. Most people can do it in minutes. |
| Whole valve (body and head) | The body leaks, the pin is seized or damaged, or you are changing the radiator or valve style | Needs the system drained or isolated. Best done by a plumber. |
Most modern TRV heads screw on with a standard M30 x 1.5mm collar, so a new head will fit many bodies. Some makes, such as Danfoss RA-type valves, use a different fitting and need a matching head or an adaptor. Take a photo of the valve, or the old head, when buying.
If you are changing the valve body, the new valve must fit your pipework. Read can I replace one type of radiator valve with another? and check the radiator tails (what are radiator tails?). Valves come in angled, straight and corner versions, so choose the one that matches how the pipe meets the radiator.
Types of TRV
| Type | How it works | Best for |
|---|---|---|
| Standard (wax or liquid sensor) | A sealed sensor expands and contracts with the room temperature to open and close the valve. No batteries. | Simple, reliable, inexpensive control |
| Programmable (electronic) | Battery-powered head with its own schedule, set on the valve | Rooms with a regular routine, no hub needed |
| Smart TRV | Connects to an app (and sometimes voice assistants) to control each room, often with a hub | Homes that want room-by-room schedules and remote control |
Whichever you choose, TRVs only control each radiator. They do not replace a good room thermostat and timer.
Are smart TRVs worth it?
They can be, but they are not automatically better.
- Good fit: a home with rooms used at different times, such as a home office, spare room or a bedroom that is only warmed in the evening. Scheduling room by room avoids heating empty rooms.
- Less value: a small flat or a home where every room is used at the same time. A standard TRV set sensibly does the same job for far less.
- Costs: smart heads cost several times as much as a basic head, and some need a hub and batteries.
Savings depend on how you use your heating and how well the system is balanced. A smart TRV on an unbalanced system or with the boiler running too hot will not fix those problems. See can TRVs reduce heating bills? for how TRVs save money, and what temperature radiators should be set to for target room temperatures.
TRVs on towel rails and in bathrooms
Towel rails behave differently from a standard radiator, so think before fitting a TRV.
- A TRV closes when the room is warm. That is the point on a bedroom radiator, but a towel rail is there to dry towels. Once the bathroom reaches temperature, a TRV will shut the rail off, and your towels will be cold.
- Option 1: use a manual valve and control the rail with the heating timer, so it runs when you need it.
- Option 2: fit a TRV but set it higher (for example 4–5), so it keeps the rail on for longer.
- Option 3: use an electric or dual fuel towel rail with its own timer and thermostat, so the towels dry independently of the boiler.
- Steam and splashes: keep the TRV head clear of showers, and check the valve finish matches the rail. Browse our towel rail valves and TRVs.
How to fit a new TRV head
- Set the new head to its maximum setting so it is fully open. This makes it easier to fit.
- Unscrew the old head and remove it.
- Check the pin in the valve body moves freely.
- Screw on the new head and hand-tighten the collar. Do not use tools.
- Set to 3 as a starting point, then adjust to the room.
Fit the head horizontally if you can. Mounted vertically, it reads the hot air rising from the radiator and shuts the valve too early. If the head is hidden behind a curtain or cover, use a model with a remote sensor.
Leave one radiator without a TRV control. In the room with your main wall thermostat, keep the radiator valve fully open or use a manual valve, so the TRV does not fight the thermostat. Heat pump systems have their own rules, so ask your installer before changing TRVs on one.
Do I have to fit TRVs?
Building Regulations expect TRVs on radiators in most rooms of homes with new or replacement heating, except in the room with the room thermostat. Replacing like-for-like valves is not usually a problem, but if you are having a new boiler or heating system fitted, your installer should specify them.
Frequently asked questions
How long do TRVs last?
Commonly 10–15 years, although they can stop working sooner if the pin sticks or the system contains a lot of sludge.
Can I replace a TRV head myself?
Yes. Replacing the head does not open the water circuit, so there is no draining. Replacing the valve body does, so use a plumber.
Why is my TRV stuck on?
The pin is probably stuck down or the sensor has failed. Remove the head and check the pin, and replace the head if the pin is free.
Why is my radiator cold at the bottom but hot at the top?
That points to sludge in the radiator, not the TRV. See does flushing radiators improve efficiency.
Do all TRV heads fit all valves?
No. Many use the standard M30 x 1.5mm thread, but some makes need a matching head or an adaptor. Check the make of the valve before you buy.
Will new TRVs reduce my heating bill?
They can, mainly by letting you turn down rooms you do not use and by closing as soon as a room is warm. The size of the saving varies, so do not expect a fixed percentage.
Need new valves for a towel rail or radiator? Browse our towel rail valves and TRVs, or contact us on WhatsApp with a photo of your current valve and we will help you match it.
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