Vaillant Comfort Mode and Flashing C on a Vaillant Boiler

James Elston
Written by James Elston
Updated on 17th May 2024
Posted on 3rd November 2023
Topic: Boiler Advice

Valliant offers a huge range of boiler options to benefit different needs. These include combi boilers, system boilers, and regular boilers that are energy efficient and come with loads of features and great warranties.

They have played a massive part in home heating over the years, and the ‘Comfort Mode‘ they have developed is supposed to increase heating efficiency and user comfort.

But does comfort mode save energy or use more? Let’s take a look at why the Vaillant comfort mode may leave your bank account more uncomfortable in the long run.

Looking for a new Vaillant boiler? See the latest Vaillant boiler prices here

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

What is the Vaillant Comfort Mode Pre Heat Setting?

The Vaillant Comfort Mode is designed to guarantee a warm and comforting home exactly when you would like it most. In contrast, traditional heating systems activate at the scheduled time, often resulting in a significant wait before reaching your desired temperature.

This delay can leave you feeling colder as the heating system catches up. However, it does use more energy. This is because it keeps the secondary heat exchanger on despite many people thinking this mode will save energy bills and gas bills. Unfortunately, this is not the case.

How To Turn Vaillant Comfort Mode On or Off

Vaillant Comfort Mode is a specialised setting designed to provide consistent heating whilst This mode adjusts the boiler’s operation, maintaining a comfortable temperature within the home.

However, it does use more energy due to the keeping of the secondary heat exchanger on. So we would bear that in mind when thinking about this, leaving the comfort mode on.

What Does the Vaillant Comfort Mode Do?

The Comfort Mode offers many advantages, for example, the ability to preheat your home and maintain a stable and comfortable temperature within the house throughout the day.

Intending to enhance your comfort, this feature adjusts to the current weather conditions. For example, as the outside temperature drops, your radiators will automatically provide more warmth, ensuring your home stays at your desired temperature.

Valliant Comfort mode also helps with an extremely low waiting time for warm water when you turn a taps or shower on. If you want to set the water to the domestic hot water temperature, this mode is ideal, as it produces hot water at your fingertips.

How to turn off pre-heat on a Vaillant Boiler

Turning off the pre heat mode is simple enough on your Vaillant gas boiler. All this involves is making sure you find the control panel or thermostat settings, where users can turn off pre heat b y turning off comfort mode. .

This will make sure the boiler does not pre heat, therefore saving you money on your gas bills. In preheat mode the secondary heat exchanger stays on using more gas, so turning it off could be a good idea.

Switching this mode on is a great asset to have available as you can choose between saving money of being more comfortable in your home.

Troubleshooting ‘Flashing C’ on Vaillant Boiler

Encountering a ‘Flashing C’ on a Vaillant boiler can be a concern for many homeowners, however, Understanding these features and issues is important for effective usage and troubleshooting.

Troubleshooting steps involve checking the manual, inspecting for common errors, or contacting a professional for assistance. If the letter C is simply just showing in the display, all it means is that comfort mode is switched on, in turn meaning that the preheat is switched on.

Why you should get a Vaillant boiler service

Getting a Vaillant boiler service every year plays a pivotal role in ensuring the optimal functionality of Vaillant boilers. Scheduled inspections and cleaning prevent potential issues and prolong the lifespan of the boiler.

It is recommended that you get your boiler serviced at least once every 12 months, in order to keep the warranty on your boiler.

However, if you want maximum protection for your boiler, then getting a boiler cover plan that includes the annual boiler service costs is the option that many people go for. This will make sure your boiler is always working up to standards, ultimately avoiding huge repair costs in the future.

Efficient Use of Vaillant Boilers

To maximise the benefits of Vaillant boilers, users should not only activate the Comfort Mode but also practice energy-conscious habits, such as setting appropriate temperatures. Lowering your thermostat setting is a simple yet effective method for optimising your hot water heating system.

Even a modest 1-degree Celsius adjustment can really influence your heating costs. In most cases, maintaining a comfortable indoor room temperature within the range of 19-21 degrees Celsius is a wise choice for most households.


Understanding Vaillant Comfort Mode and addressing the ‘Flashing C’ issue on Vaillant boilers can indicate many issues.

We would advise either checking the manual or getting in contact with a professional engineer who can help fix this issue. If you get a boiler cover plan, there is instant access to a 24/7, 365 UK-based helpline that would cater to your needs if you have any problems.

Keeping your boiler maintained is one of the most important things to do for you to avoid any serious problems with it in the future. The comfort mode will not help you save money, however, it is a beneficial mode that will pre heat your home to the required temperature for your comfort.


What should I do if my Vaillant boiler shows a ‘Flashing C’?

If your Vaillant boiler displays a ‘Flashing C,’ it could indicate a fault. Refer to the boiler manual for troubleshooting steps or contact a qualified technician for assistance as they should be able to work out exactly what the problem may be and find a solution.

How can I switch on Comfort Mode on my Vaillant boiler?

Access the control panel or thermostat settings of your Vaillant boiler settings and select the Comfort Mode option for optimised heating.

What are the benefits of Vaillant Comfort Mode?

Vaillant Comfort Mode offers you the ability to maintain a stable, comfortable temperature within your house, with access to hot water on demand with no wait, and automatically changes the temperature on your radiators when the temperature drops.

Why is regular boiler servicing essential for Vaillant boilers?

Regular maintenance ensures optimal functionality and prevents potential issues that can lead to huge unwanted repair costs further down the line. It can also mean that your boiler will last as long as it can without experiencing any serious issues.

What can I do for efficient use of Vaillant boilers?

Setting appropriate temperatures, insulating your home, and adopting energy-conscious habits contribute to the efficient use and maximum benefits of Vaillant boilers.

Ultimately, comfort mode on your Valliant combi boiler will require more energy use and may even lead to a higher gas bill. However, if you switch to ‘eco mode’ it will save money and save energy overall.

Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 3rd November 2023
Topic: Boiler Advice

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

Buy a new boiler in minutes

Instant online quotes. Nationwide next-day fitting

Get my fixed price
Get a great price on a Which? Best Buy boiler online in 20 seconds
  • Over 15,000 boiler installed
  • Rated Excellent on Trustpilot
  • Fair, fixed and final prices
  • No pushy salespeople
  • Next-day installation
  • 0% deposit interest-free finance
Next-day fitting available until 2pmGet a quote now >