Maximising Efficiency and Saving Money

You'll often find one of two scenarios with many heat pump installations.

One is that during the handover of your new system, you will be a bit overwhelmed with the amount of information given verbally and on paper, or that you will get a very quick demonstration of the thermostat and be told not to touch anything else!

Well, the latter could be a good idea if the installer has completed the commissioning sequence we are about to attempt to explain. But in reality, it is highly likely they haven't really fully commissioned your system to its full effectiveness or efficiency at all!

Many people look for the most efficient heat pump possible according to the badge rating with little appreciation of the controls, installation, or commissioning of the unit. They assume that if the unit has good statistics it will automatically give them great efficiency and low running costs. In actual fact, the unit makes nowhere near as much difference as how it's installed and controlled.

Even if it is installed well, if it's not commissioned properly, it could absolutely ruin the system’s COP (efficiency)! As I say, this is very rarely done, and it’s the part where you may be able to pick up some crucial adjustments to totally transform your system performance.

OK, before you do this, you may want to ask your installer if they have already done this or if they can do it first. Please only progress if you're confident in doing so — if you change too many settings you may have to pay your installer to come back and fix it.

Understanding Weather Compensation

The key thing to understand when you're trying to maximise the efficiency of heat pumps or condensing boilers is that the lower the flow temperature, the higher your heat pump COP (or efficiency).

Now, 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 mild weather, the thermostat will keep switching the heat pump on and off to prevent overheating – which wastes energy. You don’t drive your car at 70mph and 0mph to average 35mph, right?

To minimise flow temperature throughout the year, all heat pumps should use a feature called weather compensation.

Weather compensation simply measures the temperature outside and adjusts the required flow temperature: cold outside = hotter radiators, warm outside = cooler radiators. This minimises cycling and keeps your system running at maximum efficiency.

The fine-tuning of these flow temperatures relative to the outside temperature is where hidden efficiencies lie.

Preparing to Recommission

Before starting, check that your system has weather compensation functionality (most modern heat pumps and quality boilers do). To confirm for your specific unit, speak to your installer or check your manual.

Step 1: Turn All TRVs and Room Thermostats to Max

To see if your system is putting too much or too little energy into the house, we’ll remove other controls from the equation. Turn all TRVs and thermostats up to their maximum so they don’t limit flow.

If the property is too hot, reduce flow temperatures. If it’s too cold, increase them. If some rooms are hotter than others, your system needs balancing.

Step 2: Turn Down the Weather Compensation Curve

Every appliance’s weather compensation controls are different. Here’s an example: as outside temperature drops, the system increases flow temperature along a “heating curve.”

If your home is too warm, you need to lower this curve — reducing the slope lowers the flow temperature. For most systems, this can be adjusted by changing a single curve number in the settings.

Keep reducing slightly until your indoor temperature stays stable around your target (e.g., 21°C).

Some installers disable weather compensation altogether to avoid callbacks — this is a huge mistake. Find the compensated option and turn it back on.

We recommend using small wireless thermometers like Govee or Sonoff sensors to monitor temperatures across your home.

Pro tip: Do this when it’s cold outside (around 0°C). If you set the curve when it’s mild, you’ll need to readjust later.

Some systems also let you set maximum and minimum flow temperatures. In that case, configure them for your coldest and mildest outdoor temperatures (e.g., -3°C and 16°C).

Step 3: Controlling Your System

Once you’ve lived with your new settings for a few days and have a stable curve, it’s time to reintroduce your controls — wisely. Focus on three things:

• Minimising setbacks
• Minimising zoning
• Minimising third-party control interference

Minimising Setbacks

Setbacks are temperature drops between “day” and “night.” 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.

Minimising Zoning

Turning off rooms (zones) restricts radiator surface area and forces higher flow temperatures, reducing COP. Keep zones open where possible to spread heat evenly and maximise efficiency. Learn more in our video: Why Not to Zone Heating Systems.

Limit Third-Party Controls

Once setbacks and zones are optimised, reintroduce TRVs and thermostats only as temperature limiters, not target controllers. Set them slightly above your desired room temperature so they only prevent overheating.

Bonus Pro Tips

How much control is needed depends on how advanced your system’s weather compensation is. Most heat pumps use basic compensation, while high-end systems (Viessmann, Vaillant, NIBE, etc.) feature advanced weather compensation.

Advanced weather compensation maintains constant low flow temperatures automatically, without frequent thermostat signals. It can also use parallel shifting — lowering the curve slightly for night-time comfort and efficiency.

Some systems even include room feedback (internal influence), where the system slightly adjusts the flow temperature based on indoor readings. This helps fine-tune comfort while keeping efficiency high.

Hot Water Temperatures

Your cylinder temperature should depend on your storage size. If it rarely runs out, you can lower it to around 48°C for better efficiency. Make sure your system occasionally runs an anti-legionella cycle to 60°C.

Wrapping Up

If you’ve tried any of these steps and seen improvements — or have tips we missed — let us know in the comments!

And remember: if you want an engineer who truly understands this process, visit the Heat Geek Map to find an installer trained in these advanced techniques.