Heat Pump Thermostat Settings

Room temperature, room thermostats, and zoning (and when to move on to flow temperature)

Heat pump systems usually have two different “temperatures” in play:

Room temperature vs flow temperature

Room temperature (comfort)

• This is the air temperature inside your home (°C).

• It’s measured by a room thermostat (or a room sensor).

• It determines whether the system should keep heating because the home isn’t warm enough.

Flow temperature (heat delivery)

• This is the temperature of the water being sent to radiators/underfloor heating (°C).

• It determines how much heat the system can deliver to the house.

This guide is about room temperature control (thermostats and zoning).

If you can’t reach your target room temperature even though the heating is “on”, you’ll likely need the flow temperature guide.

What a room thermostat does on a heat pump

A room thermostat is simply a temperature sensor with a target.

• If the room is below target: it calls for heat (heating demand ON)

• If the room is at/above target: it stops calling for heat (heating demand OFF)

With many heat pumps, the system may still use weather compensation to decide how it runs in the background, but the thermostat(s) still decide whether there is demand.

Zoning explained (this is where most confusion happens)

“Zoning” means you can heat different parts of the home independently. The way this is done depends on your system type.

1) Underfloor heating: usually lots of zones (room-by-room thermostats)

Most UFH systems have:

• A thermostat in each room/zone

• Actuators on a manifold that open/close loops for that room

How it controls the heat pump

• If any zone is calling for heat, the UFH controls ask the heat pump to run.

• If no zones are calling, heating demand stops.

Common UFH zoning problem

• Too many zones turned down/off → not enough open loops → poor heat delivery and unstable running.

2) Radiators with TRVs: often one main thermostat for the whole house

Many radiator-based heat pump systems have:

• One main room thermostat (or the heat pump controller acting as one)

• TRVs on radiators to trim individual room temperatures

How it controls the heat pump

• The main thermostat controls heating demand for the whole system.

• TRVs can reduce heat into rooms, but they do not replace the main thermostat.

Critical rule

• The room with the main thermostat must not be “starved” of heat (e.g., TRVs shut down in that room), or the system can behave badly.

3) Manufacturer controller “room sensor” setups

Some homes use the heat pump’s own controller/sensor as the reference room temperature:

• Good if it’s in a representative living space

• Problematic if it’s in a hallway/utility area

In these cases, homeowners often end up “controlling” comfort using TRVs/zone thermostats—this can work, but it’s easier to misconfigure.

Target room temperatures for testing (use these first)

If your home feels cold, don’t change lots of settings. Test simply:

• Living areas: 20–21°C

• Bedrooms: 17–19°C

• Bathrooms: 21–22°C

Set the relevant thermostat(s) and leave it alone for several hours (especially with UFH).

Common misconfigurations that stop a home heating properly

• Main thermostat in a cold hallway (system keeps running, comfort still poor)

• TRVs closed in the thermostat room (system never satisfies the target properly)

• UFH zones turned down/off so far that most loops stay closed

• Multiple thermostats/controllers “fighting” (one asks for heat, another shuts it down)

• Thermostat placed near a heat source, sunlight, or draught (bad readings)

What to do if it’s cold: the correct order

Step 1 — Increase room thermostat target

⬆️ Increase by 1–2°C and wait.

If the house warms up: you’ve fixed it.

Step 2 — If the home won’t reach target temperature

If thermostats are calling for heat but rooms stall below target:

➡️ Go to your flow temperature guide (heat delivery issue, not thermostat issue).

Step 3 — If radiators/UFH are cold

If there’s little/no heat output at all:

➡️ Go to the Heat Pump Breakdown Helper.

Which Heat Pump Control Type Do I Have?

Most homes fit one of these three control setups. Tick the one that matches your home best.

✅ Option 1: Underfloor Heating with Multiple Room Thermostats (Zoned System)

You likely have this if:

• ✔ You have underfloor heating

• ✔ There is a thermostat in most rooms

• ✔ Each room can be set to a different temperature

• ✔ You have a UFH manifold with small white/grey actuators

How your system works

• Each room thermostat controls its own zone

• The heat pump runs when one or more zones call for heat

• Turning one room up does not affect others

Common mistake

• Too many zones turned down or off → system struggles to deliver heat

➡️ Use the thermostat in the room that feels cold.

✅ Option 2: One Main Room Thermostat + Radiator TRVs (Whole-House Control)

You likely have this if:

• ✔ You have radiators

• ✔ There is one main thermostat in the house

• ✔ Radiators have TRVs (numbered valves)

• ✔ Only the main thermostat turns heating on/off

How your system works

• The main thermostat controls the entire heat pump

• TRVs only fine-tune individual rooms

• The thermostat room is the reference room

Critical rule

• The room with the main thermostat must not have its radiator restricted by TRVs

➡️ Use the main thermostat to test and adjust temperature.

✅ Option 3: Heat Pump Controller Acting as the Thermostat

You likely have this if:

• ✔ There is no separate wall thermostat

• ✔ Temperature is set on the heat pump controller

• ✔ The controller shows “room temperature”

• ✔ It may be in a hallway or utility room

Common with:

• Mitsubishi

• Daikin

• Panasonic

• Vaillant (some setups)

How your system works

• The controller measures temperature where it is located

• TRVs or zone thermostats often end up controlling comfort instead

Watch out

• If the controller isn’t in a living space, comfort can be misleading

➡️ Adjust the controller temperature and check zoning/TRVs carefully.

Still Not Sure?

Ask yourself:

• “If I turn this temperature up, does the whole house respond, or just one room?”

• One room only → zoned system (UFH or room thermostats)

• Whole house → single thermostat or controller-based control

What to Do Next

• If you’ve identified your control type:

  • Set room temperature targets (see below)

  • Wait several hours

• If rooms won’t reach target temperature:

  ➡️ Heat Pump Flow Temperature Explained

• If radiators or UFH are cold:

  ➡️ Heat Pump Breakdown Helper