Radiator controls
The numbers are not degrees, they should not all be on 5, and the one in your hallway probably should not have one at all. Here is how they actually work.
Get my fixed priceTwo valves, two jobs
Every radiator has a valve at each end and they do completely different things. Getting them confused is why half the radiators in Britain are unbalanced.
The detail
A wax capsule. As the room warms, the wax expands, pushes a pin down and squeezes the valve shut. As the room cools it contracts and the valve opens again. There is no electricity, no battery and nothing to program, which is why a decent TRV lasts fifteen years and a cheap one still lasts ten.
It also means the valve senses the air around the valve head, not the room. Put a sofa in front of it or hang a curtain over it and it will read the warm pocket it has made for itself and shut off with the room still cold.
| Setting | Roughly | Sensible for |
|---|---|---|
| Snowflake | 7°C | Frost protection in an empty house |
| 1 | 10°C | A garage or an unused room |
| 2 | 15°C | Hallways, landings, a cool bedroom |
| 3 | 20°C | Living rooms and most bedrooms. Start here. |
| 4 | 23°C | A bathroom, or somebody who feels the cold |
| 5 | 26°C | Almost nobody, almost never |
These are approximate and vary between manufacturers. Turning a valve higher does not warm the room any faster — it only raises the point at which it stops.
Water is lazy. It takes the shortest route back to the boiler, so the radiator nearest the boiler gets hot in five minutes and the one at the end of the run never quite does. The fix is not a bigger boiler. It is throttling the lockshield on the near radiators so the far ones get their share.
A properly balanced system runs at a lower flow temperature for the same comfort, and a condensing boiler is meaningfully more efficient the lower its return temperature. Balancing is free efficiency and it is the thing most installers skip.
Every install includes balancing the system before we leave. If you want TRVs adding they are £42 a valve, and we will tell you honestly which radiators should not have one.
The two things people blame on valves
An unbalanced circuit and a sludged panel look like a broken TRV from the sofa. Neither is.
Questions
No, and this is the single most common misunderstanding in home heating. They are relative settings, not temperatures. Very roughly: the snowflake is frost protection at about 7°C, 1 is around 10°C, 2 is 15°C, 3 is 20°C, 4 is 23°C and 5 is 26°C.
Turning a TRV to 5 does not heat the room faster. It heats it to a higher final temperature, and then keeps it there, which costs you money.
Almost. Building Regulations require thermostatic control on radiators in rooms that do not contain the main room thermostat, on any new or replacement installation.
The exception is the room where your wall thermostat lives, usually the hall. That radiator should have a plain lockshield at both ends, or the two controls fight each other and the boiler short-cycles.
That is sludge, not a valve problem. Magnetite settles at the bottom of the panel and blocks the flow. A TRV will not fix it and neither will bleeding it.
Bleeding fixes the opposite symptom — cold at the top, warm at the bottom. That is air.
The valve body has to come off, which means draining down at least part of the system. It is a plumbing job rather than a gas job, so legally you may, but most people underestimate the draining.
We fit them at £42 a valve while we are there for the boiler, which is cheaper than a separate visit from anyone.
In a house where rooms are genuinely used at different times, yes — a spare bedroom that never gets heated is real money saved. In a house where everyone is in the same two rooms, the payback is very long.
They also need the boiler to modulate properly, and a load-compensating control. We would rather sell you a good standard TRV on every radiator than a smart one on three.
TRVs are £42 each fitted while we are there, and balancing is included whether you add them or not.
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