TRVs let each room hold its own temperature. They seize with age, usually in whichever position they were left over the summer, and the result is a room that either overheats or never warms. Most can be freed rather than replaced.
Check this first – it is free
- Take the head offThe plastic top usually unscrews or unclips. You do not need to drain anything.
- Find the pin underneathA small metal pin protruding from the valve body.
- Press itIt should move freely and spring back. A few millimetres of travel.
- If it is stuck downThe valve is closed and that radiator will never warm up. This is the commonest cause of one cold radiator.
- If it is stuck upThe valve is open and that room will overheat regardless of the setting.
- Work it gently freeGrips or a small adjustable spanner, a drop of penetrating oil, patience. Not force – the pin will snap.
- Refit the headWith the valve fully open, so the head engages correctly.
Before assuming sludge, balancing or an undersized radiator, take the head off and check the pin. It costs nothing, it takes thirty seconds, and it frequently is the answer.
Why they seize
Inside a TRV body is a pin that the head presses on. Left in one position through a whole summer with no movement, the pin binds – corroded, or simply bound by deposits from the system water.
So the failures are seasonal and predictable:
- Discovered in October, when the heating goes on and one room does not warm up.
- Stuck closed is more common than stuck open, because most people turn radiators down in spring.
- Worse on older systems with more magnetite in the water.
- Worse in hard water, where deposits add to the problem.
- Worse on cheap valves, which have tighter tolerances and poorer materials.
The prevention costs nothing: each autumn, before the heating season, wind every TRV fully open and fully closed a few times. Five minutes for a whole house, and it prevents most of these.
When they need replacing
| Finding | Action |
|---|---|
| Pin stuck but frees with gentle persuasion | Usually fine. Exercise it annually |
| Pin seized solid, will not free | Replace the valve body |
| Head broken or stripped | Replace the head only, if a compatible one is available |
| Valve weeping from the gland | Sometimes a gland repack; frequently replace |
| Very old valve, obsolete pattern | Replace, and check the body thread and pipe centres |
| Bidirectional flow needed | Some older valves are flow-direction sensitive. Modern bidirectional valves remove the problem |
| No TRVs at all | Fitting them is one of the better value improvements available |
Replacing a valve body means draining down that part of the system, or freezing the pipe locally, so it is a slightly bigger job than swapping a head. Several at once is more efficient than one at a time.
Fitting them properly
- Leave one radiator without a TRV. Normally the one in the room with the main thermostat. If every radiator has a TRV and they all close, the pump circulates against closed valves and the boiler short-cycles.
- Position matters. A TRV reads the air around it. Behind a curtain, above a radiator cover, or in a draught from a door, it reads the wrong temperature and shuts the radiator off while the room is still cold.
- Remote sensor versions exist for exactly those positions, and they solve it properly.
- Horizontal or vertical heads depending on the installation, so the head is not sitting in the radiator’s own rising heat.
- Rebalance afterwards, because the flow characteristics change.
- Set them sensibly per room and explain the numbers to whoever lives there – the numbers are temperature settings, not power levels, and a great many people turn them to maximum to heat a room faster, which does not work.
Turning a TRV to 5 does not heat the room faster – it heats it to a higher final temperature. The radiator is fully open either way until the room approaches the set point. It is the single most common misunderstanding about TRVs and it costs people money every winter.
Smart TRVs
Battery-powered heads that schedule each room individually and talk to a hub or a smart thermostat.
Where they genuinely earn their cost: a house where rooms are used very differently – a home office occupied on weekdays, a spare room used occasionally, bedrooms wanted cool at night and warm in the morning. The per-room scheduling is a real benefit in that situation.
Where they do not: a house where the whole downstairs is occupied at the same times. Standard TRVs plus a decent thermostat achieve nearly the same result for a fraction of the cost.
The practical considerations: they need batteries changing, they are considerably more expensive, they may depend on a hub or a service, and they still cannot do anything about a boiler that is not modulating – see smart heating controls.
One radiator cold? Take the TRV head off and press the pin before anybody quotes for anything.
Questions we get asked about this
Why is one radiator always cold?
Most often a seized TRV. Take the head off and press the pin underneath – if it is stuck down, the valve is closed. It is the commonest cause and the cheapest to fix.
What do the numbers on a TRV mean?
Target room temperatures, not power levels. Turning it to 5 does not heat the room faster, it heats it to a higher final temperature. This is the most common misunderstanding about them.
Should every radiator have a TRV?
All but one. The room containing the main thermostat should have plain valves, so there is always a flow path when every other TRV closes.
How do I stop them seizing?
Each autumn, wind every TRV fully open and fully closed a few times before the heating season. Five minutes for a whole house and it prevents most seizures.
My TRV is behind a curtain and the room is always cold.
It is reading the warm air trapped behind the curtain and shutting off early. A remote-sensor TRV solves it, or move what is blocking it.
Are smart TRVs worth it?
In a house where rooms are used very differently, yes. Where the whole house is occupied at the same times, standard TRVs and a good thermostat get you nearly the same result for far less.
What happens when you call
Call and describe it
You speak to an engineer, not a call centre. Most jobs can be narrowed down on the phone.
We look at it properly
A real diagnosis before a price, and a straight answer if it is not worth doing.
A written quote
Itemised, so you can see what you are paying for.
The job, and the paperwork
Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
- Norwich
- Wymondham
- Dereham
- Attleborough
- Aylsham
- North Walsham
- Cromer
- Diss
- Loddon
- Long Stratton
- Watton
- King's Lynn
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.