How to Make the Most of Your Heat Pump This Winter

So, you’ve done all your research and decided to have a heat pump installed to provide your home with energy efficient, low carbon heating. Not only will you enjoy a warm and cosy home but the feel-good factor of knowing you are reducing your carbon footprint and managing your energy use. Your installer should set your heat pump up to work as efficiently as possible before handing the system over to you. It’s very important that your heat pump is set up properly to ensure your running costs are as low as possible and you are toasty warm. 

You may feel a bit overwhelmed with the amount of information you are given both verbally and in the form of a manual during the handover. The manual should include instructions on how to adjust common settings on your heat pump. If you are not happy with your heat pump system’s performance and don’t feel confident to make changes yourself, it’s a good idea to ask your certified installer to check your installation and explain the settings. 

Contrary to what most people think the actual heat pump unit makes nowhere near as much difference as to how it’s installed and controlled. You should not assume that choosing a heat pump based on it’s badge rating or good statistics will automatically mean that it gives you great efficiency and low running costs. Even if it’s installed properly, if it’s not commissioned very well it could result in the system not operating as efficiently as it should.

Once you feel confident that you understand how the various settings work for your heat pump system you can manage your own energy use. If you are not sure that you know what you’re doing, it’s probably best to seek advice from your installer.

The most important thing to understand when you’re trying to maximise the efficiency of heat pumps is that the lower the flow temperature, the higher your heat pump Coefficient of Performance (COP). COP is a measure of a heat pump's efficiency at a specific moment, defined as the ratio of the useful heat produced to the electrical energy it consumes. A heat pump with a COP of 3 produces 3 units of heat for every unit of electricity it uses while a higher number indicates greater efficiency.

This is when you need to understand how weather compensation works. The temperature your radiators need to be to maintain your desired room temperature isn't the same all year round. For example, your radiators might need to be 50°C when it's -2°C outside, but only 35°C when it's 12°C outside in spring and autumn. If they’re still running at 50°C during a mild weather, the thermostat will keep switching the heat pump on and off to prevent overheating, which wastes energy.

It’s worth checking that your heating curve is set correctly as sometimes installers will set the control curve higher to make sure your house is warm in winter. You may be able to reduce your heating curve quite a bit without making your home feel too cold. 

Before adjusting your heating curve also known as ‘outdoor weather compensation’ you should check that your system has weather compensation functionality (most modern heat pumps do). To confirm this for your specific unit, speak to your installer or check your manual.

In a nutshell, weather compensation measures the temperature outside and adjusts the required flow temperature: cold outside equals hotter radiators, warm outside equals cooler radiators. This keeps your system running at maximum efficiency. 

Fine-tuning your system

Step 1: Isolate the system

To check whether your system is putting too much or too little energy into the house set all room thermostats to their maximum setting and turn all thermostatic radiator valves (TRVs) up to their maximum flow position. This allows you to see the raw output from the weather compensation curve. It’s best to make these adjustments when it’s cold outside as this is when the system is working hardest and any issues are most obvious. 

Step 2: Adjust the weather compensation curve

If some rooms are too cold, you need to increase the system's heat output. This is done by raising the weather compensation curve. This will increase the flow temperature for a given outside temperature, making the rooms warmer.

If some rooms are too hot, you need to decrease the system's heat output. This is done by lowering the weather compensation curve. This will lower the flow temperature, reduce overheating, and save energy.

Make the adjustments in small increments and then wait for your system to stabilise before you make another change. 

Check the weather compensation curve. Some systems use a single curve value while others have a more detailed graph or options for maximum/minimum flow temperatures. Adjust the relevant settings on your system’s controller which is usually found under “service settings” or “installation controller.”

Finally, you may need to balance the system if some rooms are significantly warmer or cooler than others. To balance the system, a separate adjustment is required after the weather compensation curve is correctly set. 

Step 3: Stabilise and re-enable other controls 

Once you have made these adjustments, allow the system to run for a while to see if your desired indoor temperature (21∘𝐶) is being maintained. 

When you have a stable curve, you can then re-enable your room thermostats and TRVs. 

At this point you can fine-tune individual rooms by turning down room thermostats to act as a high-limit control or use TRVs to control the temperature in specific rooms. Use TRVs and thermostats only as temperature limiters and not target controllers. Ideally, set them slightly above your desired room temperature so they only prevent overheating. 

To minimise setbacks and maintain efficiency, keep the system running for longer periods and use smaller temperature setbacks (the difference between day and night settings) rather than turning the system off completely. A large setback (e.g. 21°C → 16°C) effectively turns your heat pump off overnight, forcing it to work harder in the morning. Instead, use a small setback (2–3°C) to keep thermal mass warm and flow temperatures low.

It's a good idea to keep rooms open to spread heat evenly to maximise efficiency rather than turning off rooms which restricts radiator surface area and forces higher flow temperatures. 

Leaving your heat pump on for longer periods doesn’t increase your overall running costs because the heat pump can run more efficiently, offsetting the longer running period.

It’s worth bearing in mind that lowering the heat pump’s flow temperature reduces the reaction time of the heating system. This means it takes longer to warm the house in cold weather, but it will also have a big impact on your running costs. That’s why it’s a good idea to turn it down in small one-degree increments until your home is too cold for you and then turn back up in one-degree increments until your house feels comfortable. 

The amount of control needed will depend on how advanced your system’s weather compensation is. Most heat pumps use basic compensation while high-end systems such as Viessmann and Valliant feature advanced weather compensation. If you have a system with advance weather compensation it will maintain constant low flow temperatures automatically, without frequent thermostat signals. It can also use something called parallel shifting which involves lowering the curve slightly for night-time comfort and efficiency.

There are some systems that even include room feedback which is where the system slightly adjusts the flow temperature based on indoor readings. This helps fine-tune comfort while keeping efficiency high.
Other factors to consider making the most of your heat pump system

The temperature of your hot water cylinder should depend on your storage size. If you rarely run out of hot water, you can lower it to around 48°C for better efficiency. However, UK building regulations advise that water cylinders need to regularly reach temperatures of more than 60°C. This is to protect against Legionella bacteria, which causes Legionnaire’s disease, a severe form of pneumonia. Heat pumps are usually set to complete this function either daily, weekly, or permanently. If your bills are high, you might find that the timer has been set to do this job too often. For most homes it’s safe to use this function once a week and you certainly don’t need to do this every day if you’re at home on a regular basis.

In the UK, one of the most asked questions about our gas central heating systems is whether we should keep them on all the time or turn them on and off as and when needed. It is common practice to turn our heating systems on in the morning, off when we go to work and back on again in the evening when we return home. However, it’s better to keep heat pumps on all the time but lower the temperature if you’re out or asleep. This is because if the temperature of your home drops by a few degrees, your heat pump has to work a lot harder to warm it again. Air temperature can drop by more than 5°C overnight in the winter, which will reduce the heat pump’s efficiency because it has to work harder to heat water to a high temperature. In the case of heat pumps, it’s important to make sure that your heat pump isn’t trying to heat your hot water or the house overnight when outside air temperatures are significantly lower unless you’re using a time of use tariff when electricity is cheaper. 

Another way to make the most of your heat pump system is to have your electricity come from a renewable energy source. You will be able to maximise your savings and improve your carbon footprint even more if you combine solar panels with a home battery which will let you store free, renewable electricity to power your heat pump. By being less reliant on using electricity from the grid you will bring down your electricity bills even more. The biggest advantage of a home battery comes in when you also have a time of use tariff. These tariffs encourage you to use your energy outside of peak times, with lower energy costs as a result. 

You may have chosen not to upgrade your radiators when you had your heat pump installed but are now finding the radiators not big enough to heat some of the rooms. If your radiators aren’t big enough it won’t matter how big and powerful your heat pump system is. Gas boilers typically run at 75°C so your radiators will be fine but as the water temperature in your heat pump system can drop to 45°C, which is quite normal for heat pumps, you may well need bigger radiators. Having larger radiators means there will be more surface area to circulate heat. You can get double or triple radiators that don’t take up extra wall space.  

Although heat pumps can perform down to -15°C or lower, there may come a point when the heat pump’s output isn’t enough for you. Fortunately, we don’t see these sorts of temperatures very often. 

When temperatures drop dramatically like this, the ‘heating boost’ or ‘heating comfort’ setting on your heat pump panel can help. The heat pump uses an additional heater element to add energy to the system, until the temperature outside is within the expected limits. The heat pump doesn’t use this extra power for long, so it shouldn’t add much to your running costs, even over a whole year. 

You should read your manual to make sure you have the heating boost set to come on only when the temperature outside is low enough. 

If you find yourself having to use this function regularly you need to speak to your installer as it might indicate that your radiators are too small or your heating curve isn’t set right. 

If you want to make the most of your heat pump this winter, make sure you have read the manual which came with the heat pump and that you understand the basics of both the control system and the heat pump itself. Taking the time to do this could save you money as well as keep you warm.

If there is something seriously wrong with your heat pump, the control screen will tell you. Don’t ignore any warnings you see on the control screen. Check the fault log and see if you are getting recurring fault messages and if you are, speak to your installer and manufacturer to find out what’s causing them. It’s far better to sort these issues out quickly, than run the risk of your heat pump breaking down in the depths of winter. One common fault to watch out for is a ‘heating blocked’ message, which might mean that your heat pump is running at temperatures that are too high. 

It's not always a problem with the heat pump itself, sometimes it’s a problem with the central heating system. Faulty pumps, valves or sludge and dirt in the radiators can all cause problems, which at first appear to be an issue with the heat pump. 
Consider installing water treatment and a filter in your central heating system to avoid having long-term problems with the heat pump which could be expensive.

If your installer is unable to help you for some reason, it’s worth speaking to the manufacturer. They often employ technicians who have more experience in solving issues with your specific model.