Room thermostat or TRV
Updated: October 2026
A British Gas page will tell you a thermostatic radiator valve does the same job as a room thermostat and that you do not need both. If you are replacing a boiler, or you let a property, that sentence is the expensive one. A room thermostat or TRV is not a choice of substitutes. One can turn the heat source off. The other only throttles a single radiator. This page follows the BEAMA summary of Approved Document L, then places the Danfoss listings in our [Danfoss thermostat comparison](/hub/thermostats/danfoss-thermostat) on the correct side of that split. Thread sizes stay on the RA page. Dial numbers stay on the how-to page. We are the Products Compared editorial team, and we did not test a boiler. A qualifying purchase can earn a commission at no extra cost to you.
A British Gas page will tell you a thermostatic radiator valve does the same job as a room thermostat and that you do not need both.
A British Gas page will tell you a thermostatic radiator valve does the same job as a room thermostat and that you do not need both. If you are replacing a boiler, or you let a property, that sentence is the expensive one. A room thermostat or TRV is not a choice of substitutes. One can turn the heat source off. The other only throttles a single radiator. This page follows the BEAMA summary of Approved Document L, then places the Danfoss listings in our Danfoss thermostat comparison on the correct side of that split. Thread sizes stay on the RA page. Dial numbers stay on the how-to page. We are the Products Compared editorial team, and we did not test a boiler. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Job | Power | Schedule | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Danfoss Danfoss Redia RA click | Radiator head | None in the bullets | No | 9.6 | about £16.99 | View offer |
 Danfoss Danfoss RAS-C2 | Radiator head | None in the bullets | No | 9.4 | about £30.18 | View offer | |
| Alternative |  Danfoss Danfoss TPOne | Room thermostat | 230 V | Flexible schedule in the bullets | 7.4 | about £32.49 | View offer |
On this page
Two different switches
A TRV head senses the air around one radiator and closes that valve as the room warms. The Redia and the RAS-C2 do that with a liquid sensor and no batteries. The Eco does it with a Bluetooth schedule, still on one radiator, and still only within about 10 m. None of them tells the boiler that the house is warm. If every head closes and the boiler has no separate interlock, the boiler can keep running with nowhere useful to send the heat. That is why a head swap, however neat, is not the same control as a wall stat. A room thermostat sits on a wall and calls for heat, or stops calling, for a zone or for the whole system. In this set the TPOne, the TP5000Si and the RET2001 are those wall listings. The TP5000Si title says hardwired, not RF, and UK reviews describe a backplate swap. The TPOne is 230 V on its listing, with a thin sample of eight reviews. The RET2001 does not state a voltage in the raw file. The BasicPlus2 is a further 230 V wall listing at £80 whose only bullet claims Wi-Fi, without a UK review that shows the app. A wall stat can be part of switching the boiler off. A cracked head in the spare room cannot. One reference-room stat plus heads elsewhere is the pattern the English guidance describes.
The England pattern
When a heat generator is replaced, BEAMA’s Part L 2022 heating-controls guide, reading Approved Document L Volume 1 for England, expects thermostatic room controls: a thermostat in a reference room, and a TRV on every other emitter. The TRV does not go in the thermostat’s room. If it did, the head could close, the reference room would stay cooler than the stat believes, and the rest of the house would shut down early. BEAMA’s siting note makes the same point from the other direction: do not put the room thermostat in a room already fitted with radiator thermostats. About 1.5 m, in free air, not above a radiator, is the placement. How you choose the number on the head is on how to set a Danfoss thermostat. Take a typical English semi. The hallway holds the wall stat at about 1.5 m, clear of the front door and not above a radiator. The living room, bedrooms and landing get TRVs. The hallway radiator stays without a TRV so the stat can still see an open emitter. British Gas’s consumer explainer says you do not need both a room thermostat and TRVs. That clashes with the BEAMA summary. Follow the BEAMA PDF if you are doing work that has to meet the English guidance. Danfoss’s GB Part L page says the requirements are not identical in every nation of the UK. Working TRVs do not have to be replaced for their own sake. BEAMA’s installer factsheet notes that, for England from 15 June 2022, a TRV that already works is not a mandatory swap.
Boiler Plus and interlock
Boiler interlock means the controls can shut the boiler and the pump down when there is no demand, rather than leaving them to run against closed valves. A liquid head on one radiator does not create that interlock by itself. It only stops water at that radiator. Danfoss lists time control, boiler interlock, TRVs and one Boiler Plus measure as separate items on its Part L page. If your system has no interlock today, a Redia at £16.99 will not add it. Boiler Plus, for a gas combi in an existing English dwelling, still asks for one extra measure: flue-gas heat recovery, weather compensation, load compensation, or a qualifying smart control. A Redia or RAS-C2 is not that measure. The Eco in this comparison is not automatically that measure either. Bluetooth in the same room, with UK reviews that describe a slow connection, is not the same thing as a qualifying smart control on the boiler. A landlord replacing a boiler needs the pattern of one reference-room stat plus TRVs elsewhere, plus whatever Boiler Plus measure the combi still lacks. The buying guide is where you match a listing to that job once you know which device is missing.
Which listing is which
Put the TPOne, the TP5000Si and the RET2001 on the wall side of the decision. The TPOne at £32.49 is the cheaper programmable hardwired listing, with the limit of eight reviews and one report of a fault with no seller reply. The TP5000Si at £280 has 4.3 from 394 reviews and a title that says it is not RF. Buy that listing only as a like-for-like wall replacement if the price is acceptable, not as a better radiator head. The RET2001 at £52.05 needs an electrician when the terminals do not match the conductors, which is what happened in the UK review with two wires and three terminals. Put the Redia, the RAS-C2 and the Eco on the other radiators, not in the reference room. The Redia is the best value RA click spare at £16.99. The RAS-C2 is the dearer mechanical head, and the top pick in this set when you want that sensor rather than the lowest price. The Eco is the scheduled head, with the Bluetooth limit. The best Danfoss radiator thermostat page ranks those heads and leaves the £280 stat out. The BasicPlus2 does not belong on a radiator neck. If you are replacing the boiler, opening unknown wires, or working on a bathroom circuit, use a competent person. Like-for-like accessory replacement is often outside a Building Regulations notice, but BS 7671 still applies, and the person doing mains work has to be competent. None of these seven is a plug-in stat on a 13 A plug.
Common questions
Can TRVs replace the wall thermostat?
No. A TRV limits one radiator. A room thermostat can stop the call for heat to the boiler or the zone. BEAMA’s reading of the English guidance keeps both, in different rooms, when a heat generator is replaced. A page that says you only need TRVs conflicts with that summary.
Why not fit a TRV in the thermostat’s room?
Because the head can shut the radiator in the only room the stat is measuring. The stat then thinks the house is warm enough while other rooms are still cold, or the opposite if the sensor is in a bad spot. Leave that room without a TRV, and fit heads on the others. About 1.5 m of free air, not above a radiator, is where BEAMA puts the wall stat.
Does a new head meet Boiler Plus on a combi?
No. Boiler Plus asks a gas combi in an existing English home for one extra measure, such as weather compensation, load compensation, flue-gas heat recovery, or a qualifying smart control. A liquid Danfoss head is not that measure. This Eco ASIN is not automatically that measure either.
What is boiler interlock in one sentence?
Boiler interlock is the control arrangement that switches the boiler and pump off when the rooms are not calling for heat, so they do not run against closed radiator valves. A single TRV head does not provide it. Danfoss treats interlock as separate from the TRVs on its Part L page.
Which Danfoss listings are wall stats?
The TPOne at £32.49, the TP5000Si at £280, and the RET2001 at £52.05. The BasicPlus2 at £80 is also a wall listing, with an unproven Wi-Fi bullet in this file. The Redia, RAS-C2 and Eco are radiator heads. The £280 unit is not a better head.
Do I have to replace TRVs that already work?
Not for their own sake. BEAMA’s note on the English changes from 15 June 2022 says working TRVs need not be replaced just because the guidance exists. Replace a head that has failed, or add heads where emitters have none, and leave a sound valve alone.
Does this differ in Wales or Scotland?
Danfoss says the Part L picture is not the same in every UK nation. The BEAMA summary used here is the England pattern for a replacement heat generator. Check the rule for Wales, Scotland or Northern Ireland before you treat an English boiler job as universal. The product split, a head on the radiator and a stat on the wall, does not change with the border.
Related pages
Sources
Public UK sources for Approved Document L, BS EN 215, Danfoss product data, and Part P. Listings are the amazon.co.uk captures for these seven ASINs, not a live reload on 17 October 2026. Prices on amazon.co.uk move.
- BEAMA Part L 2022 heating controls (retrieved 17 October 2026)
- Danfoss GB, Part L (retrieved 17 October 2026)
- BSI, BS EN 215:2019 (retrieved 17 October 2026)
- Danfoss Eco data sheet (retrieved 17 October 2026)
- Danfoss Eco support (retrieved 17 October 2026)
- Danfoss RAS-C2 013G6040 (retrieved 17 October 2026)
- Danfoss Redia 015G5120 (retrieved 17 October 2026)
- IET Part P FAQ (retrieved 17 October 2026)