Arotherm Plus Hot Water Modes (Eco, Normal, Balance, Sweet Spot)

Arotherm Plus Hot Water Modes TL;DR

Vaillant gives you three official hot water modes: Normal, Eco and Balance. On top of those, I’ve also tested a fourth DIY option I call Sweet Spot mode, created using the Noise Reduction setting.

• Normal Mode – Fastest, Least Efficient (no limits on the compressor)

• Eco Mode – Slowest, Most Efficient (compressor output limited around 50%)

• Balance Mode – A Mix of Normal and Eco (same limits as Normal and Eco)

• Sweet Spot Mode – A DIY Middle Ground (compressor limited, but not as much as Eco)

I’ve tested all four modes on my 5 kW aroTHERM Plus paired with a 250 L Mixergy cylinder. Here’s how they actually behave in practice.

Note: this article (updated September 2025) forms part of a wider series of Vaillant Arotherm information and guides.

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

Table of Contents

This article about hot water modes is a comprehensive read.

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

Why Hot Water Modes Matter

Coming from a gas combi boiler, this takes some getting used to. A combi gives you hot water on demand, effectively limitless as long as the boiler can keep up.

With a heat pump it’s different, you need to preheat and store hot water in a cylinder. Just like a combi boiler, when the heat pump is heating water, it isn’t heating the house. But because the power output of a heat pump is much lower than most combis, it takes longer to reheat the cylinder. So whilst the heating would have been off for just the length of a shower with the combi, it will be off for the entirety of heating water in the cylinder.

This is a big adjustment and mindset shift. But it does make you appreciate the value of hot water more, and the energy (and money) it takes to create it.

On top of that, cylinder sizing and mixing become part of the equation. A bigger cylinder means more hot water but longer reheat times. Storing at a higher temperature and mixing down at the tap can stretch usable litres, but efficiency drops as stored temperature rises. I’ve covered this in detail in Hot Water Cylinder Sizing and Mixing.

Vaillant provides three official hot water modes — Normal, Eco and Balance. On top of these, I’ve also tested a fourth DIY option, Sweet Spot mode, which I created using the Noise Reduction feature.

In this article we’ll look at each mode in detail, with real-world data showing how each one actually performs.

Normal Mode – Fastest, Least Efficient

In Normal mode, the heat pump runs at full output for the whole hot water cycle.  The compressor is not limited, so goes full beans at 120 rps.

• Test run: ~180 L heated (29→100%), target 48 °C, outside 3 °C

• Took ~60 minutes

• Peaked at 7–8 kW heat output for ~2.5 kW electrical input (both the peak output and input would be higher on bigger Arotherm models, see tables later)

Pros:

• Hot water back quickly

• Good for busy households when you need speed

Cons:

• Higher peak electrical demand

• Least efficient mode

Eco Mode – Slowest, Most Efficient

Eco mode reduces the compressor to 50 rps on my 5 kW model. Electrical input stays low, but run times stretch out.

• Test run: ~190 L heated (24→100%), target 48 °C, outside 3.6 °C

• Took ~130 minutes

• Heat output capped at ~3 kW, input just above 1 kW

Across almost 700 Eco hot water runs over a year, my system delivered a water only SCOP of ~3.8 across the whole of 2024, which makes it the most efficient of the modes by some distance. See A Review of 700 Heat Pump Hot Water Runs in 2024 for the full dataset.

Pros:

• Lowest electrical input

• Highest efficiency (SCOP ~3.8 across whole year)

• Works well with solar PV

Cons:

• Longest run time

• Can cause comfort issues in less insulated homes

• Slow on small heat pumps paired with large cylinders in winter

Problems with Eco Mode (on Smaller Heat Pumps & Large Cylinders)

Eco mode is great for efficiency, but when you’ve got a smaller aroTHERM unit and a big cylinder, the downsides become more obvious:

• With low compressor output and a large hot water volume (200 L+), reheat times stretch out, sometimes double what they’d be in Normal mode.

• When the outside temperature drops, output falls further. In winter near freezing, a 5 kW unit in Eco mode might only manage ~2.3–2.7 kW output, dragging runtimes even longer.

• If you let the cylinder run very low, the long recovery can be painful, so more waiting, more time without heating.

• Because the heat pump is tied up with hot water for so long, the house heating is off for longer too, leading to dips in indoor temperature.

Full write-up: The Problem with Eco Hot Water Mode

Balance Mode – A Mix of Normal and Eco

Balance mode starts at full pelt like Normal (120 rps). Once the cylinder return temperature reaches 45 °C it drops into Eco / low compressor mode (50 rps).

• Test run: ~205 L heated (18→100%), target 51 °C, outside 18 °C

• Took ~85 minutes

• Starts at ~7 kW output, then falls back to ~3 kW

Pros:

• Quicker than Eco but less efficient

• More efficient than Normal

• Hands-off compromise without changing settings

Cons:

• Still not as fast as Normal if you want a full tank quickly

• Personally I think the sequence is wrong way round (Eco first then Normal would make more sense)

The reason why I think Balance is the wrong way around is that it’s in Eco, right at the start of the hot water run, when the flow temperatures are really low, that you get all the juicy COP.

But with Balance starting in Normal, you miss out on all that, so it’s kinda useless.

You can look at the investigations and all the date behind these thoughts in my Sweet Spot Hot Water Mode article.

In fact, I even went as far as re-creating a Reverse Balance mode (Eco then Normal), which I catchily called “Sweet Spot Reverse Balance Mode”.

Sweet Spot Mode – A DIY Middle Ground

Sweet Spot isn’t an official option. It’s a DIY mode I created using the Noise Reduction setting, which caps the compressor at 80 rps. That puts it neatly between Eco (lower compressor speed) and Normal (full output).

You can read how I came up with Sweet Spot and all the trials and data behind it in this article: Vaillant Arotherm Sweet Spot Hot Water Mode.

• Test run: ~190 L heated (24→100%), target 48 °C, outside 3.2 °C

• Took ~90 minutes

• Output averaged ~4.5 kW, input ~1.5 kW

Pros:

• Faster than Eco, more efficient than Normal

• A good middle ground

Cons:

• Needs manual scheduling

• Less efficient than Eco

👉 Note: You won’t see Sweet Spot listed in the installer menu. It’s a DIY setup. Follow the instructions in the Sweet Spot article. And see the How to Change Hot Water Mode section for the official options.

How to Change Hot Water Mode

You can select which mode you want to run via the VWZ AI Heat Pump Controller, but you’ll need to go into the Installer Menu. Press both upper buttons at the same time to get to the menus.

• The default code to access the installer menu is 17

• Once in, look for DHW Mode

• Then choose either Eco, Normal or Balance

⚠️ Be careful. The installer menu contains settings that can affect your whole system. If you don’t know what you’re doing, stay out of here.

Disclaimer: I accept no responsibility for any issues you run into by poking about with settings. With great power comes great responsibility.

👉 Note: Sweet Spot mode isn’t in this menu. It’s a DIY method I created using Noise Reduction. See the Sweet Spot Mode article for details

How to extend hot water run times past 2 hours

When you drop into Eco mode for hot water you reduce how hard the compressor needs to work. This lowers both the electrical input and the heat output compared to Normal mode.

The trade-off is that hot water run times become longer. On smaller models you might even hit the default 120 minute limit.

To get around this you can adjust settings on the indoor controller (Installer Menu → Domestic Hot Water menu):

• Max cyl charge time: set to Off

• Cyl. charge. anti-cycl time: set to 0 min

With “Max cyl charge time” disabled, runs can extend past two hours.

The “Cyl. charge. anti-cycl time” setting controls how long the heat pump waits to start a hot water run again after pausing at the limit. For example, if you kept “Max cyl charge time” at 120 mins, setting anti-cycl to 30 mins would allow the heating to run for 30 minutes before hot water tried to complete.

The obvious downside of allowing longer hot water runs is that your house will not be heating during this time. A heat pump can only do one job at a time. If you live in a house with high heat loss you may not want the heating off for such long periods.

The Heat Pump Hot Water Golden Rules

These rules aren’t theory. They come from almost three years of experiments testing different modes, temperatures, and starting points from empty and full cylinders. They’re the route to the most efficient and cost-effective way of heating hot water with a heat pump.

From The Heat Pump Hot Water Golden Rules, here are five rules that underpin all of this:

1. Reheat from as empty / cold a cylinder as possible (use high hysteresis)

2. Choose the lowest target hot water temperature you can get away with

3. Use Eco mode (or another low-compressor mode)

4. Schedule reheats when it’s warmer outside

5. Make the most of off-peak tariffs (this is almost always the cheapest option)

How long will a reheat take?

Reheat time depends on cylinder size, the amount of water you are reheating, and which mode you are in. My system is a 5 kW aroTHERM Plus with a 250 L Mixergy cylinder.

From my test runs:

These figures are specific to my system, but they give a good sense of the trade-off between speed and efficiency.

Here’s a quick reference table showing approximate times to heat various amounts of water from 10 °C to 50 °C based on a variety of heat outputs (kW).

Output Across Modes and Models

From the datasheet outputs highlighted in the Top of the SCOPs article and my own investigations, I have created this quick reference table:

This shows how much difference there is in DHW output between modes. A bigger unit with more output means quicker hot water recovery, especially in Eco mode.

Hot Water Modes Compared (3 official + 1 DIY)

Note: All test data above is from my 5 kW aroTHERM Plus with a 250 L Mixergy cylinder. The Balance run heated ~205 L to a 51 °C target at 18 °C outside. Larger or smaller systems will give different run times, but the relative differences between modes still hold true. See the Output Across Modes and Models table above for how Eco, Sweet Spot and Normal scale with bigger heat pumps.

Cylinder Sizing & Mixing

Cylinder size and mixing temperature have a big impact on usable hot water. The MCS standard recommendation and rule of thumb is 40–45 litres per person per day, but if you can fit a bigger cylinder, do it. In my view these recommendations fall well short of reality in a busy household. School runs, work, football, gym, dance classes, it all adds up.

If you store water hotter (say 50–55 °C) and then mix it down to 40–42 °C at the tap, you effectively stretch the usable litres. The trade-off is lower efficiency at higher storage temps.

A bigger cylinder also lets you treat it as a giant heat battery. You can charge it up on a cheap off-peak tariff and then use that hot water through the day.

Example:

Mixergy Cylinder — Setting the Record Straight

Some people claim that Mixergy cylinders are sub-optimal compared to conventional cylinders when used with heat pumps. One installer said that, but in over three years of use, I’ve seen nothing but strong performance from mine. I dug into this in Mixergy Heat Pump Performance and here’s what I found.

• I’ve been using a 250 L Mixergy direct cylinder since early 2022. First on direct electric with solar PV diversion, then later adding the Mixergy heat pump kit (plate heat exchanger, external pump and interface).

• When paired with my 5 kW Vaillant aroTHERM Plus, the Mixergy performs just as well, if not better, than most conventional cylinders. At 12 °C outside I achieved ~480 % efficiency (COP ~4.8) heating to a ~45 °C target.

• Even when using higher target temperatures (like 48 °C) in colder conditions (<10 °C outside), performance stayed strong (>400 %) using Eco mode.

The Mixergy has been a perfect fit across my renewable journey. First with direct electric and solar diversion, then with the heat pump kit.

One of Mixergy’s unique selling points is that you get the full cylinder volume as usable hot water. So my 250 L Mixergy is a true 250 L, unlike many conventional cylinders.  You can see the result of that in The Mixergy Usable Hot Water Capacity Test.

Which hot water mode is the cheapest?

This is the inevitable question. The truth is, there isn’t one single “cheapest” mode. It depends on your tariff and timing.

As detailed in The Heat Pump Hot Water Golden Rules, off-peak tariffs almost always outdo COP. The real win is combining the two: aim for the best COP and the cheapest unit rate when you schedule your hot water runs.

Or better still, time them with your own solar generation. A mid-afternoon Eco run to self-consume excess PV is about as cheap as it gets.

If you’re not sure what time-of-use tariffs are, I’ve explained them here: What Are Time-of-Use Tariffs?. I’ve also compared options in detail in Best Heat Pump Tariff.

And if you want to see how COP and SCOP figures actually translate into pounds and pence on your bill, take a look at SCOP Versus Pounds and Pence.

👉 Note: Tools like Havenwise now let you automatically schedule hot water runs to the cheapest periods in a time-of-use tariff like Octopus Agile or Octopus Cosy. You can also control your heating remotely to aim for the lowest running costs.

Final Thoughts

Vaillant only gives you three official hot water modes: Normal, Eco and Balance. On top of that, I’ve tested a fourth option — Sweet Spot mode — which I created myself using the Noise Reduction feature.

• For efficiency, Eco wins

• For speed, Normal is unmatched

• For a balanced compromise, Sweet Spot works well

• Balance tries to combine modes, but in my view the sequence is the wrong way round

These results are from my 5 kW aroTHERM Plus with a 250 L Mixergy cylinder. If you’ve got a bigger heat pump or a smaller tank, your timings and outputs will look different, but the trade-offs between speed and efficiency will still apply.

Big shout out to the guys at Open Energy Monitor for their heat pump monitoring system.  This article would never have been possible without their kit.

You can monitor my system here: https://emoncms.org/energystatsuk

My system is also part of the growing list of systems taking part in the https://heatpumpmonitor.org/ project.

Hot Water Modes FAQ

Which hot water modes does Vaillant officially provide?

Three: Normal, Eco and Balance. Sweet Spot is a DIY method I created using Noise Reduction.

Which hot water mode is the most efficient?

Eco. Across nearly 700 runs on my system, Eco delivered a SCOP of ~3.8 across the whole year.

Which hot water mode is the fastest?

Normal. It runs the compressor flat out until the cylinder is hot.

What is Balance mode on a Vaillant heat pump?

A hybrid of Normal and Eco. It starts at full power, then drops into Eco once the return temperature hits 45 °C.

What is Sweet Spot mode on a Vaillant heat pump?

It is not an official option. I created it by setting Noise Reduction to cap the compressor at 80 rps. This lands neatly between Eco and Normal.

Why does Eco mode take so long on a Vaillant heat pump?

If you have a small heat pump with a large cylinder, Eco will be slow. In that case Normal or Sweet Spot may be better choices when you need hot water more quickly.

How do you change the hot water mode on a Vaillant heat pump?

Through the VWZ AI Heat Pump Controller, in the installer menu (code 17). Then select DHW Mode. Be careful though. If you do not know what you are doing, stay out of the installer settings.

What is the best hot water mode for a Vaillant heat pump?

It depends on your priority. If you want maximum efficiency, use Eco. If you want speed, use Normal. For a good compromise, Sweet Spot works well.

Which hot water mode is the cheapest to run?

There is not one single cheapest mode. It depends on tariff and timing. As detailed in The Heat Pump Hot Water Golden Rules, off-peak tariffs almost always beat COP. The real saving comes from combining the two, or timing runs to match your solar PV. See Best Heat Pump Tariff for more detail.