The controls that work best with a heat pump are the manufacturer’s own controller set up for weather compensation, with a room sensor giving gentle feedback on the flow temperature, rather than a standard smart thermostat switching the heat pump on and off. A heat pump is most efficient when it runs for long periods at the lowest flow temperature that keeps you warm. Good controls make that happen. Poor controls fight it.
This guide covers the main control types, how they affect efficiency, what Building Regulations require, and the setup we recommend for most UK homes.
What Is the Difference Between a Manufacturer Controller and a Smart Thermostat?
A manufacturer controller talks directly to the heat pump and adjusts its flow temperature continuously, while most third-party smart thermostats can only send an on or off signal. That difference decides whether the heat pump can modulate smoothly or has to stop and start.
Manufacturer controllers use the brand’s own communication link. Vaillant’s sensoCOMFORT, for example, connects over an eBUS interface and can show energy consumption, energy yields and efficiency figures for heating and hot water. Third-party thermostats such as Nest or tado are designed around boilers, and while they list heat pumps as compatible, the connection is often a simple switch.
| Control type | How it talks to the heat pump | Controls flow temperature? | Best use |
|---|---|---|---|
| Manufacturer controller (wired or wireless) | Proprietary link such as Vaillant eBUS | Yes, continuously | Main control for almost every system |
| Manufacturer room sensor or remote unit | Proprietary link | Yes, feeds room temperature into the flow calculation | Living area reference room |
| Third-party add-on built for heat pumps | Brand-specific interface to the heat pump’s controller | Depends on brand and model | Remote access, scheduling and monitoring |
| Standard smart thermostat on a relay | On or off signal only | No | Limited; can cause cycling if it is the main control |
| Basic room thermostat | On or off signal | No | Simple backstop or holiday protection |
How Does Weather Compensation Work on a Heat Pump?
Weather compensation on a heat pump sets the flow temperature from the outdoor temperature using a heating curve, so the water going to your radiators is only as warm as the weather demands. On a mild day the flow temperature drops. On a freezing day it rises towards the design temperature set by your installer.
Vaillant describes the heat curve as the link between flow temperature and outdoor temperature for a target room temperature. Its example shows a flow of 40°C at an outdoor temperature of −15°C with a curve setting of 0.4 and a 20°C room target. That is a well-designed, low-temperature system. A home with smaller radiators needs a steeper curve.
Weather compensation matters more on a heat pump than on a boiler because heat pump efficiency falls as flow temperature rises. MCS installation standard MIS 3005-I states that weather compensation should be enabled where it would optimise system efficiency. Your installer should set the curve at commissioning, and the Energy Saving Trust advises the same. We cover the general principle in our separate guide to weather compensation.
What Are Load Compensation and Room Influence?
Load compensation adjusts the flow temperature based on how far the room temperature is from its target, and room influence is the heat pump version of this, where a room sensor nudges the weather-compensated flow temperature up or down. Weather compensation looks outside. Load compensation looks inside. Room influence blends the two.
A 2017 BRE report for government defined weather compensation as sensing outside temperature to limit the water temperature leaving the heater, and load compensation as using an internal sensor to judge heat demand. Most heat pump controllers now combine both.
Vaillant’s sensoCOMFORT is a clear example. Its room temperature modulation setting has three options:
| Setting | What it does | Effect on the heat pump |
|---|---|---|
| Inactive | Flow temperature follows the heat curve | Steady, weather-led running |
| Active | Adjusts the flow temperature based on the current room temperature | Corrects for solar gain, cooking or wind while still modulating |
| Expanded | Adjusts flow temperature and also switches the zone on and off | Behaves more like a thermostat; can add stops and starts |
Other brands use different names for the same idea, such as auto adaptation. The principle is the same: use the room reading to fine-tune the flow temperature rather than to switch the heat pump off.
Why Can an On/Off Smart Thermostat Hurt Heat Pump Efficiency?
An on/off smart thermostat can hurt heat pump efficiency because it stops the heat pump each time the room reaches its target, which causes more start-ups and often leads to higher flow temperatures to recover the lost heat. A boiler copes with this reasonably well. A heat pump does not.
Heat Geek, a UK heat pump training provider, notes that heat pumps have considerable losses on start-up and that the compressor needs time to reach its best efficiency. It estimates that a heat pump loses about 2.5% efficiency for every extra degree of flow temperature. Short bursts at a high flow temperature combine both problems.
Boiler-style habits make it worse. Setting the heating to come on twice a day with large setbacks means the heat pump has to recover quickly, which pushes up the flow temperature. The Energy Saving Trust advises that leaving a heat pump on for longer periods does not increase running costs because it runs more efficiently.
This does not mean third-party products are useless. Some, such as tado’s Heat Pump Optimizer X, connect to specific heat pump brands through their own interfaces rather than a basic relay, and offer scheduling, energy monitoring and room-guided optimisation. Check exactly how any product connects to your model before buying.
Do Heat Pumps Work With OpenTherm?
Some heat pumps can accept an OpenTherm signal, but many use the manufacturer’s own protocol instead, so you cannot assume an OpenTherm thermostat will modulate your heat pump. OpenTherm is widely used by modulating gas boilers, and Google states that its 3rd-generation Nest Learning Thermostat and Nest Thermostat E support OpenTherm boilers. That does not mean an OpenTherm thermostat can modulate your heat pump.
Vaillant’s heat pump controls, for example, use eBUS. Other brands use their own links too. If you want a third-party thermostat, ask your installer whether it can talk to the heat pump through a supported interface or whether it would only switch it on and off. If it is the latter, the manufacturer controller should stay in charge of flow temperature.
Should You Use TRVs and Zoning With a Heat Pump?
You can use TRVs and zoning with a heat pump, but they work best as limiters in a few rooms rather than as the main way of controlling the house. Each TRV that closes cuts flow and water volume, which can make the heat pump cycle and push up the flow temperature in rooms still heating.
Heat Geek’s example shows why. Cutting two rooms from 21°C to 18°C raised the mean water temperature needed in the other radiators from 46°C to 51.5°C, because heat escapes through internal walls into the cooler rooms. It recommends TRVs left fully open and modest setbacks of about 2°C for heat pumps, while accepting that some homes do need zoning.
A common approach is:
- No TRV, or a TRV set fully open, in the room with the main controller or room sensor.
- TRVs in bedrooms set a little lower as upper limits, not daily on/off switches.
- Smart TRVs used sparingly, with schedules that avoid shutting most radiators at once.
- Underfloor heating zones kept to the minimum the layout needs.
Your installer must check that enough water stays open when valves close. If it does not, the design may need a volumiser or buffer.
What Can Heat Pump Apps and Energy Monitoring Show You?
Heat pump apps can show you flow and room temperatures, energy used and, on many models, an estimate of heat delivered and efficiency. That helps you spot a curve set too high or unexpected immersion use.
Built-in figures are usually estimates. For a more accurate picture you need a dedicated electricity meter and heat meter on the heat pump. HeatpumpMonitor.org, an open-source project, publishes real-world performance from hundreds of systems monitored with MID-certified electricity and heat meters, and is a useful benchmark for your own figures.
| Monitoring option | What it measures | Accuracy |
|---|---|---|
| Manufacturer app | Estimated electricity use, heat output, temperatures | Indicative; varies by brand |
| Smart meter in-home display | Whole-house electricity use | Accurate, but does not separate the heat pump |
| Dedicated electricity sub-meter | Heat pump electricity only | Good |
| Sub-meter plus heat meter | Electricity in and heat out, giving real efficiency | Best available |
How Do You Schedule a Heat Pump for a Time-of-Use Tariff?
You schedule a heat pump for a time-of-use tariff by running hot water and a slight temperature boost in the cheap periods, then easing back in the expensive ones, while leaving the heating on steadily rather than switching it off. Large swings cancel out the saving by forcing a high flow temperature to recover.
Octopus’s Cosy Octopus tariff, for example, has three cheaper windows at 04:00 to 07:00, 13:00 to 16:00 and 22:00 to midnight, and a peak rate from 16:00 to 19:00. It is open to homes with a heat pump and a compatible smart meter. A sensible schedule might heat the hot water cylinder in the early morning and afternoon windows, raise the room target by about 1°C in the early afternoon and trim it by 1°C to 2°C in the evening peak. Tools such as tado’s Balance add-on, at £5.99 a month, can shift heating automatically.
What Do Building Regulations Say About Heat Pump Controls?
In England, Building Regulations require that when a heat generator such as a boiler is replaced, or a heating system is installed in a new home, each room should have thermostatic room controls that let the heating output be adjusted separately. This came in with the 2021 edition of Approved Document L (paragraph 5.20) from 15 June 2022, and it covers heat pumps replacing a boiler.
| Rule | What it means for a heat pump install |
|---|---|
| Room-by-room temperature control (ADL para 5.20) | Each room needs a thermostatic control, commonly a room thermostat or sensor in one room and TRVs elsewhere |
| Exception: single-storey open plan | Where the living area is over 70% of the floor area, one control can serve it |
| Exception: similar adjacent rooms | Two neighbouring rooms with a similar use can be treated as one zone |
| Exception: not technically feasible | For example very low heat demand homes |
| Maximum 55°C design flow | New and replacement wet heating systems in England should be designed for a flow temperature of 55°C or lower |
This is why many heat pump installs still have TRVs even though an open design suits the heat pump better. A good installer meets the rule and then sets TRVs so they rarely close. Wales, Scotland and Northern Ireland set their own building standards, so the exact wording differs. A new 2026 edition of Approved Document L comes into force for new homes in England from 24 March 2027.
What Is the Best Control Setup for a Heat Pump?
The best control setup for most heat pumps is the manufacturer’s controller running weather compensation, a room sensor in the main living area with gentle room influence, TRVs kept mostly open, and steady schedules with small setbacks. Anything else should add to that, not replace it.
- Weather compensation on, with the curve set as low as keeps the house comfortable.
- Room influence switched on at a moderate level, not full on/off control.
- Heating left on through the day with a setback of about 1°C to 2°C overnight.
- Hot water scheduled into cheaper tariff windows where you have them.
- TRVs used as upper limits in bedrooms and spare rooms.
- Energy data checked each month, ideally with proper sub-metering.
Expect to fine-tune the curve over the first winter. Lower it a step if rooms run warm, and raise it only if the house cannot hold temperature in cold weather. If you want help choosing controls for a new install or setting up an existing system, book a survey with HomeKOG.
