Turn Off Preheat on Vaillant Combi Boiler to Save Energy

If your boiler seems to fire up occasionally even when nobody is using hot water, you’re not imagining things. These brief bursts of activity throughout the day usually make many homeowners start wondering whether those extra cycles are quietly adding to their energy bills.

In many cases, the answer lies in a feature called preheat. Some make it a hack to turn off preheat on Vaillant combi boiler in an attempt to save on their energy bills.

We’re here to tell you that while the savings aren’t usually dramatic, adjusting the right boiler settings can contribute to a more energy-efficient home—particularly as energy prices remain a concern for households across the UK.

This article walks you through understanding how preheat works on Vaillant combi boilers, when it’s useful, and when switching it off makes sense for your household.

Related: How to Automate Heating Schedule with Hive for Savings

What Is Preheat on a Vaillant Combi Boiler?

Preheat is a function designed to reduce the amount of time you wait for hot water at your taps.

On many Vaillant combi boilers, the system keeps parts of the domestic hot water circuit warm and ready to respond quickly when a tap is opened. Think of it like keeping a kettle partially warmed up rather than starting from cold every time you want a cup of tea.

• In short, with the preheat switched on, hot water arrives faster.

Without preheat, the boiler has to start the heating process from scratch whenever hot water is needed. 

Importantly, this setting relates to hot water production rather than your central heating system. If you’re trying to turn off preheat on Vaillant combi boiler models, understanding how the feature works first will help you decide whether disabling it is the right choice for your home.

How Does Vaillant Comfort Mode Work?

Many Vaillant boilers refer to preheat as Vaillant comfort mode. On many models, Vaillant comfort mode is enabled by default because it prioritises faster hot water delivery over maximum energy efficiency.

When the feature is active, the boiler periodically warms the plate heat exchanger or other internal components so they’re ready when a tap is opened. Sensors monitor temperatures and trigger occasional heating cycles to maintain this readiness.

For homeowners, the result is greater convenience. Turn on a hot tap, and hot water generally arrives more quickly than it would otherwise.

However, that convenience comes with a trade-off. Because the boiler periodically reheats itself throughout the day, it consumes a small amount of additional gas compared with operating in Eco Mode or with preheat disabled.

How to Turn Off Preheat on Vaillant Combi Boiler

Although the exact process varies by model, most modern Vaillant combi boilers allow you to disable the preheat function by switching from Comfort Mode to Eco Mode.

To turn off preheat:

• Access your boiler’s hot water settings using the control panel.
• Look for an option labelled Comfort Mode, Hot Water Comfort, or Eco Mode.
• Select Eco Mode, which typically disables the preheat function and prevents the boiler from continuously keeping water warm.
• Confirm the setting if prompted and exit the menu.

Some Vaillant boilers have a dedicated Eco or Comfort button, while others require you to navigate through the digital menu. If you cannot find the option, consult your boiler’s user manual for model-specific guidance.

When adjusting your boiler settings, avoid changing any advanced installer parameters. These controls are designed for qualified heating engineers, and incorrect adjustments can affect your boiler’s performance.

If you’re unable to locate the preheat setting or want advice on improving your boiler’s efficiency, a qualified heating engineer can help ensure your system is configured correctly.

Will Turning Off Preheat Actually Save Energy?

Yes, turning off the preheat function can save energy, but the amount you save depends on your household’s hot water usage.

By switching to Eco Mode and disabling preheat, the boiler stops maintaining the reserve of hot water made possible by Comfort Mode, reducing unnecessary standby energy consumption. This can lead to lower gas usage, particularly in homes where hot water isn’t used frequently.

You are likely to see greater savings in turning off preheat or Comfort Mode if:

• You are out of the house for most of the day.
• Your household has low or occasional hot water demand.
• Hot water is typically used only at certain times, such as in the morning and evening.
• You don’t mind waiting a few extra seconds for hot water to reach the tap.

However, it’s important to keep expectations realistic. The preheat function accounts for only a small portion of a boiler’s overall energy use. Factors such as your heating flow temperature, thermostat settings, home insulation, and the efficiency of the boiler itself generally have a much bigger impact on annual energy bills.

When Should You Leave Vaillant Comfort Mode On?

While switching to Eco Mode can help reduce energy consumption, there are plenty of situations where leaving Comfort Mode enabled is the better choice.

You may want to leave Comfort Mode on if:

• Your household uses hot water frequently throughout the day.
• Multiple family members regularly shower or use hot water at the same time.
• You prefer near-instant hot water at taps and showers.
• You live in a larger property where quick access to hot water improves everyday convenience.

For many homeowners, the additional energy used by the preheat function is a worthwhile trade-off for faster hot water delivery and a more comfortable experience.

Ultimately, there is no single “best” setting. The right choice depends on your lifestyle, hot water usage patterns, and personal preferences. If you’re unsure which option suits your home, try using Eco Mode and Comfort Mode for a few weeks each and compare the difference in convenience and energy consumption.

Other Vaillant Combi Boiler Settings Worth Checking

Many homeowners focus on preheat because it’s easy to adjust, but optimising other settings can have a much bigger impact on running costs.

Consider checking the following:

Heating flow temperature

Lowering the flow temperature, while still keeping your home comfortable, can help modern condensing boilers operate more efficiently.

Hot water temperature

Make sure the temperature isn’t set higher than necessary, as excessive settings can waste energy.

Heating schedules

Review your timer or programmer settings to ensure your heating only runs when it’s needed.

Smart thermostats and controls

If your system includes smart controls or weather compensation, configuring them correctly can improve efficiency and reduce energy usage.

General system optimisation

Regular servicing and properly balanced heating controls can help maintain consistent performance and lower operating costs.

A well-configured heating system doesn’t just reduce energy bills—it can also improve comfort, extend the lifespan of your boiler, and keep the entire system running more efficiently over the long term.

For your regular boiler servicing, choose Rowlen. Our team of expert professionals can help you keep your heating system running efficiently for more years to come.

Frequently Asked Questions

Can I turn preheat back on if I don’t like it?

Yes. Most Vaillant boilers allow you to switch between Comfort Mode and Eco Mode whenever you wish. Many homeowners test both settings before deciding which best suits their household.

Book a boiler quote

Call our specialists on 020 8395 8616 or fill in our booking form.

Does turning off preheat affect central heating?

No. Preheat primarily affects domestic hot water performance. Your central heating system will continue operating normally.

Is Eco Mode the same as turning off preheat?

On many Vaillant models, Eco Mode effectively disables the preheat function. However, terminology and functionality can vary slightly between models, so it’s always worth checking the user manual.

Why is my Vaillant boiler still firing up occasionally?

Even with preheat disabled, boilers may operate briefly for reasons such as frost protection, pump protection, or routine system monitoring. Occasional activity is often completely normal.

Will turning off preheat reduce my gas bill?

Potentially, yes. Most households will see some reduction in energy consumption, but the savings are usually modest and depend on overall usage patterns.

Ready to Improve Your Boiler Efficiency?

Small boiler settings can make a noticeable difference to your energy bills—but only if they’re set up correctly for your home.

If you’re unsure whether your Vaillant combi boiler is running at its most efficient, or you simply want peace of mind that nothing is quietly wasting energy in the background, a professional check is the safest and most effective next step.

An expert boiler service from our team at Rowlen can help you:

• Identify hidden inefficiencies that increase running costs
• Optimise your settings for better performance and lower energy use
• Ensure your system is operating safely and reliably year-round

Book your boiler service with Rowlen today and make sure your heating system is working as efficiently—and cost-effectively—as it should be.

Contact us today!