Yes, you can have one thermostat upstairs and another downstairs. The change needs a separate circuit for each floor with its own motorised zone valve, a wiring centre or two-zone control, and two thermostats that both signal the boiler. In England, Approved Document L expects each heating zone to have independent time and temperature control. Any work touching the gas side of the boiler may only be carried out by a Gas Safe registered engineer.
Can you have two thermostats for upstairs and downstairs?
Yes, a separate thermostat for upstairs and one for downstairs is a normal arrangement on a wet central heating system. It is not a setting you switch on at the boiler. Each floor needs its own motorised zone valve, its own thermostat, and wiring that tells the boiler which zone is calling for heat.
A zone valve is a valve that opens or blocks the flow of heating water into one circuit. The zone thermostat drives it, and it closes again once that floor reaches its set temperature. Viessmann describes zoning as work that uses external components such as zone valves, fitted by a suitably qualified engineer, rather than something adjusted on the appliance. Two-port zone valves simply open or shut; three-port mixing valves can also adjust the flow temperature, and Viessmann advises settling that choice with the installer who has seen your system.
Two zone valves or smart TRVs: which route splits upstairs from downstairs?
Upstairs and downstairs can be separated with two zone valves and two thermostats, or with smart thermostatic radiator valves grouped into zones. The first route divides the pipework into two circuits; the second controls radiators room by room while one main thermostat still drives the boiler.
| Criterion | Two zone valves and two thermostats | Smart TRVs with one main thermostat |
|---|---|---|
| How the home is split | Upstairs and downstairs run as two circuits, each with its own switching times and its own set temperature. | Individual rooms are grouped into zones at the radiator, with one main thermostat still controlling the boiler. |
| What gets installed | A motorised zone valve per circuit, plus a wiring centre or a two-zone control linking both thermostats. | A smart radiator valve head on each radiator you want controlled, paired with a compatible smart control. |
| Pipework | Flow and return usually have to be split into an upstairs and a downstairs leg, so pipework is opened up. | No pipework split. The valve heads replace the existing thermostatic radiator valve heads. |
| Known limits | Worcester Bosch states its controls are designed for one hot water zone and one heating zone, so the control choice matters. | Worcester Bosch advises against a smart TRV in the room holding the main thermostat, as the heating can then run continuously. |
What zoning an existing heating system involves beyond a second thermostat
Zoning an existing system is pipework, valve and control work, not a thermostat swap. A thermostatic radiator valve (TRV) is the dial on a radiator that limits the temperature in that one room, and it does not give a floor its own timing. These are the parts a two-zone retrofit usually brings with it.
- A motorised zone valve for each circuit, with the heating flow split into an upstairs and a downstairs leg.
- A wiring centre or a two-zone control that links both thermostats, both valves and the boiler.
- A cable route or a wireless receiver for the second thermostat.
- An automatic bypass where one is needed. Worcester Bosch states that a correctly set automatic bypass must be fitted between flow and return if zone valves or TRVs can stop circulation completely and the boiler has no internal bypass.
- TRVs on the radiators, except the radiator in the room with the room thermostat, which Worcester Bosch says should stay uncontrolled.
- Commissioning, which includes balancing the radiators across both zones. That is part of the engineer's work, not a householder task.
Zoning cannot be set up at the boiler. Separate upstairs and downstairs control needs external parts, and those parts have to suit the boiler and the existing wiring. Treat a second thermostat as a system change rather than an accessory.
Balancing means adjusting how much flow each radiator takes, so circuits warm through at a comparable rate. Our guide on balancing radiators explains why some rooms never seem to warm up.
What the building rules in England say about heating zones
Approved Document L, Volume 1 (2021 edition incorporating 2023 amendments) applies to dwellings in England. It expects heating systems to be divided into separate control zones where solar gain, patterns of use or type of use differ significantly between parts of the home. Each zone should have independent control of both time and temperature. Upstairs and downstairs is the textbook example of that split.
For new wet heating systems, Approved Document L sets at least two independently controlled circuits where the floor area is above 150 square metres. That figure is written for new dwellings, not for a retrofit in an existing house. In an existing home the same document expects room-by-room thermostatic control when the heat generator is replaced, with zone-level control only where it is justified, such as a single-storey open plan layout where the living area exceeds 70 per cent of the floor area.
Boiler Plus applies in England and has done since April 2018. Every boiler installation in an existing dwelling must include time and temperature control plus boiler interlock, where these are not already present and working. Boiler interlock is the control arrangement that stops the boiler firing when no zone is calling for heat.
Can your existing controls run two zones, or do they need changing?
Your current control may be limited to a single heating zone. Worcester Bosch states in its support FAQ that its controls are designed for one hot water zone and one heating zone. A second heating zone therefore needs a different control arrangement rather than a second matching thermostat.
Several manufacturers publish two-zone options and wiring documents. Ideal Heating publishes Halo multi-zone wiring schematics for combi two-zone, S Plan, S Plan Plus and Y Plan systems, and lists a Halo Combi 2-Zone Upgrade and a Halo Heat and System 2-Zone Extension for the second zone. The Glow-worm Smart Wiring Centre documentation covers up to two heating zones plus a hot water zone, using two-port zone valves and two room thermostats. Baxi lists an RF Thermostat Twin Channel described as being for homes with two heating zones.
FM Power fits Worcester Bosch, Vaillant, Ideal, Baxi, Glow-worm, Viessmann and Megaflo. Which control suits your home depends on the boiler type, the existing wiring and how the pipework runs. The free home survey looks at all three before you get a written fixed price.
Who may carry out the work, and what you can check yourself
Gas work may only be done by a competent person. Regulation 3(1) of the Gas Safety (Installation and Use) Regulations 1998, as amended, states that no person shall carry out work in relation to a gas fitting unless competent to do so. Regulation 3(3) requires membership of a class of persons approved by HSE, which is the Gas Safe Register. These regulations apply in Great Britain, meaning England, Wales and Scotland; Northern Ireland has its own 2004 regulations.
HSE states that it is illegal for anyone who is not Gas Safe registered to carry out gas work. Anything touching the gas supply, the flue, seals, condensate inside the appliance or the boiler casing is work for a Gas Safe registered engineer. FM Power is Gas Safe registered.
- Boiler pressure: Worcester Bosch and Baxi both put the normal cold reading at around 1.0 to 1.5 bar, and a low reading can shut the boiler down.
- Thermostat and programmer settings: check that each zone is set to come on at the times you expect and that one zone is not switched off.
- The reset button on the front of the boiler.
- Bleeding radiators: heating off and cool, a cloth under the bleed valve, the key turned slowly anticlockwise, closed as soon as water appears, then check the pressure again.
If the gauge sits below that range, our guide on low boiler pressure explains what the reading means.
Hot water as a third circuit: what changes on a cylinder system
A home with a hot water cylinder already has one controlled circuit of its own. The Megaflo Eco Plus indirect cylinder is supplied with a cylinder thermostat, a thermal cut-out, a two-port motorised valve and a wiring centre. In an S Plan layout the cylinder thermostat and the cut-out sit in series with that zone valve. Splitting the heating into upstairs and downstairs then adds a third controlled circuit, so the wiring centre has to carry heating zone one, heating zone two and hot water.
The cylinder thermostat on a Megaflo Eco Plus is adjustable between 12 and 68 degrees Celsius. Our guide on what temperature a hot water cylinder should be set to covers that side of the system.
If the zoning work goes hand in hand with a new or replacement cylinder, our Megaflo and unvented cylinder work starts with a free home survey and a written fixed price before anything is touched.
Sources
- Approved Document L, Conservation of fuel and power, Volume 1: Dwellings (2021 edition incorporating 2023 amendments)
- Boiler Plus: new standards for domestic boiler installations from April 2018
- The Gas Safety (Installation and Use) Regulations 1998, regulation 3
- Domestic gas: frequently asked questions (HSE)
- How to add a zone to a boiler (Viessmann)
- Technical Bulletin TB 0159a: auto bypass requirements (Worcester Bosch)
- Can I use Worcester controls on multiple zones?
- Where should I install TRVs (Worcester Bosch)
- Smart heating gets smarter with zoned heating control (Worcester Bosch)
- Halo multi-zone wiring schematics (Ideal Heating)
- Halo Combi 2-Zone Upgrade (Ideal Heating)
- Halo Heat and System 2-Zone Extension thermostat (Ideal Heating)
- Smart Wiring Centre 3 installation and maintenance instructions (Glow-worm)
- Baxi RF Thermostat Twin Channel
- What to do if your boiler loses pressure (Worcester Bosch)
- What should my boiler pressure be set at (Baxi)
- How to bleed a radiator (Worcester Bosch)
- Megaflo Eco Plus unvented hot water cylinders installation manual