Vaillant Arotherm Heat Pump Guide: Weather Curve, Hot Water Modes, SensoCOMFORT, COP & SCOP

Vaillant Arotherm Heat Pump Guide: Weather Curve, Hot Water Modes, SensoCOMFORT, COP & SCOP

Introduction

If you own a Vaillant Arotherm Plus heat pump or are considering one, getting the most out of it is all about setup, monitoring, and fine-tuning.

This guide compiles key insights from Energy Stats UK to help you optimise your Vaillant weather compensation curve settings, select the best heat pump hot water settings, understand the different hot water modes, master the SensoCOMFORT controller, and accurately measure COP & SCOP.

In this Vaillant Arotherm Heat Pump Guide we’ll also cover known firmware issues, model performance differences, cycling and minimum modulation and real-world seasonal results, so you can boost efficiency, cut costs, and avoid common pitfalls.

Table of Contents

Use the Table of Contents below to jump straight to the section that matters most or scroll through at your own pace.

Vaillant Arotherm Basic Settings

If you are looking for a straightforward way to set up your Vaillant heat pump, my guide on Vaillant Arotherm Basic Settings covers everything you need to know. It explains how to set heating schedules, choose the right setback mode, understand the OT switch-off threshold, and adjust the weather compensation curve for comfort and efficiency. It also looks at Room Temp Mod options and introduces Havenwise, a smart remote optimiser that can take control of your system automatically.

Vaillant Arotherm Basic Settings

Why is my heat pump still heating when the target room temperature is exceeded?

As this is such a common question in Vaillant Arotherm forums I’m answering it specifically.

If you are used to a boiler, it can feel odd when a heat pump keeps running after the room temperature has gone past your target. A boiler is usually either on or off, but with weather compensation a heat pump works in a different way.

In Inactive and Active Room Temp Mod modes, the heat pump does not simply stop once the set temperature is reached. Instead it looks at the outside temperature and the inside temperature, and then picks a target flow temperature from the heating curve. That flow temperature is what drives how hot your radiators or underfloor are.

If the room is getting warmer than you want, the first thing to try is lowering the curve slightly. This will bring the flow temperature down and slow the heat going into the house.

The blunt alternative is to switch to Room Temp Mod: Expanded. In that mode the heat pump will switch off once the room hits the target temperature. It does work, but it is not the recommended way to run your system. With a properly set curve, Inactive or Active modes will keep your home steady and efficient.

It is also worth checking the OT Threshold. A sensible number here is around 16 °C, so the heat pump will switch off when the outside temperature goes above 16 °C and back on again when it drops below.

For a full explanation, see both of these guides:

• SensoCOMFORT Room Temp Mod: Inactive, Active or Expanded?

• Vaillant aroTHERM Weather Curve and Heating Curve Guide

You may also wish to read Heat Pump Performance for Normal People.

Heat Pump Performance for Normal People

Want to understand how a heat pump really performs in everyday life? I’ve put together a plain-English guide on heat pump performance for normal people, covering how they work, why they feel different to gas boilers, and the simple setup tweaks that make them both efficient and comfortable.

Heat Pump Performance for Normal People

Weather Compensation Curve for Vaillant Arotherm

The Vaillant weather compensation curve adjusts your system’s flow temperature according to the outdoor temperature.

• Why it matters: Lower flow temperatures mean higher COP and lower running costs.

• How to set it: On the SensoCOMFORT controller, choose a slope that matches your home’s heat loss profile and system design.

• Heek Geek Pro tip: Gradually reduce the curve value over a number of days until you are cold, then put it back up one value.

Vaillant aroTHERM Weather Curve & Heating Curve Guide

SensoCOMFORT Controls & Room Temp Mod Settings

The Vaillant SensoCOMFORT Room Temp Mod function influences how the weather curve responds to actual indoor temperature.

• Inactive: Uses weather curve only.

• Active: Blends indoor sensor feedback with the weather curve for smoother control—ideal for most UK homes.

• Expanded: Runs like Active, but also acts more like a thermostat, stopping heating when the target indoor temperature is reached.

You may also want to consider a remote control optimiser like Havenwise that can make automatic curve and temperature decisions for you as well as schedule hot water runs at the cheapest times.

SensoCOMFORT Room Temp Mod: Inactive, Active or Expanded?

Hot Water Modes Explained (Eco, Normal, Balance)

The Vaillant hot water mode comparison: Eco vs Normal vs Balance shows how each setting affects recovery time and efficiency:

• Eco mode: Slower but most efficient, capping compressor speed.

• Normal mode: Fastest recovery, highest power use.

• Balance mode: Starts like Normal, switches to Eco near target temperature.

Arotherm Plus Hot Water Modes

Hot Water Performance, “Sweet Spot” Mode and Cylinder Sizing

Analysis of real-world Eco mode COP for Vaillant Arotherm shows that Eco delivers the highest SCOP for hot water—often above 3.8—but recovery can be slow, especially with larger cylinders.  Which was explained in the The Problem With Eco Mode Hot Water Mode article.

The Vaillant Sweet Spot hot water mode guide explains how limiting compressor speed to around 80 rps achieves recovery roughly 30% faster than Eco with only a small drop in efficiency.

You may also wish to read The Heat Pump Hot Water Golden Rules which describes which are the best settings for heat pump hot water to get the best performance.

The final hot water related article that could be of interest is the Hot Water Cylinder Sizing and Mixing guide.

The Problem with Eco Hot Water Mode

Vaillant Arotherm Sweet Spot Hot Water Mode

Best Heat Pump Hot Water Settings (The Golden Rules)

Hot Water Cylinder Sizing and Mixing

5. Measuring Vaillant COP & SCOP

• COP (Coefficient of Performance): Real-time efficiency—heat output divided by electrical input.

• SCOP (Seasonal COP): Average performance over a season.
  Learn exactly how to measure Vaillant heat pump COP and SCOP using the Yield Indicator menu.
  Example: At 35 °C flow temperature, SCOP can exceed 4.4, but drops near 3.0 at 55 °C.

How to Measure Vaillant Arotherm COP

Firmware Issues & Fixes

Firmware 351.06.07 Energy Integral bug explained shows how a cycling error reduced efficiency.

• Fixed in 351.09.01 and 351.09.02—worth updating if you have an older version.

• Firmware 351.06.07 also ignores “Compr.start heat.from” after the first heating cycle.

Vaillant Arotherm Firmware 351.06.07 Problems (Energy Integral)

Performance Differences Between Models

Datasheets comparing smaller Vaillant heat pumps vs larger models performance confirm that 3.5 kW and 10 kW units are software-limited versions of the larger 5 kW and 12 kW systems.

While the hardware is similar, larger Arotherm models tend to achieve higher SCOP than their smaller counterparts.

Smaller Heat Pumps will never reach Top of the SCOPS

Real-World Winter Performance Review

From November 2024 to April 2025, a 5 kW Arotherm Plus recorded:

• SCOP Combined: 4.0

• Heating SCOP: 4.2

• Hot Water SCOP: 3.5

The third winter performance results for Vaillant Arotherm Plus also show that even during a –2.9 °C average day, heating COP stayed near 2.87. Firmware updates reduced cycling, further improving seasonal efficiency.

You may also find value looking back at my previous winter season summary articles; First Winter With My Air Source Heat Pump and Second Winter with our Vaillant ASHP.

As well as a monthly usage and performance breakdown going back to October 2022 in the Heat Pump Performance History article.

Third Winter with our Vaillant Heat Pump

Heat Pump Performance History

Use Time Of Use Tariffs to reduce running costs

Time-of-use (ToU) tariffs can significantly reduce your running costs if your Vaillant Arotherm Plus is set up to make the most of cheaper off-peak electricity rates. By scheduling hot water heating or boosting buffer storage during low-cost periods, you can improve your overall seasonal performance factor and lower bills.

We covered many of the Octopus Energy tariff options in this Best Heat Pump Tariff article.

As well as a Summary of Octopus Energy Smart Tariffs including Agile, Tracker, Intelligent Go and Cosy.

Tip: Pair ToU Tariffs with weather compensation and hot water scheduling for maximum savings without sacrificing comfort.

Best Heat Pump Tariff

Heat Pump Cycling and Minimum Modulation

Why do heat pumps cycle?  Especially more so in milder weather?

The key to understanding cycling is to understand the homes demand and the minimum modulation of your heat pump model.  Once you know those elements you can predict when cycling should start and stops.

This article: Heat Pump Cycling and Minimum Modulation goes deep into how to check your own set-up as well as data from all the various Arotherm models.

Heat Pump Cycling and Minimum Modulation

Heat Pump Myths

I know this isn’t strictly about Vaillant heat pumps, but after 3 years with mine I wanted to tackle some of the most common questions and myths people still seem to believe. If you’re curious what I found (and want to separate fact from fiction), check out my article “Heat Pump Myths Busted: Real Insights from a UK Family Home”.

In that piece I cover:

• Claims about cold weather stopping heat pumps working

• Whether running costs are really as bad as some say

• Misunderstandings about how efficient heat pumps are long-term

• What manufacturers mean by COP / SCOP, and what you can realistically expect

• And several more myths that seem to crop up over and over

If you’ve ever wondered “Is my heat pump doing enough?” or “Am I getting what I paid for?”, it’s worth a read.

Heat Pump Myths Busted: Real Insights from a UK Family Home

Vaillant Arotherm Heat Pump Guide Conclusion

By fine-tuning the Vaillant weather compensation curve, selecting the right Room Temp Mod, choosing efficient hot water modes, understanding cycling, following the hot water golden rules and keeping firmware up-to-date, you can significantly improve your Vaillant Arotherm heat pump’s COP and SCOP.

For deeper dives into each topic, explore the full set of heat pump and solar resources at Energy Stats UK.