If your Vaillant boiler stops heating water, it can be a real inconvenience. It means you or your clients are left without heating and hot water, which is especially problematic during cold weather, in homes with elderly people or children, or simply when comfort is most needed. The good news is that many of these issues have clear explanations and solutions. This guide will help you understand the possible reasons and how to fix them.
A Quick Overview of Vaillant Boilers
Understanding how Vaillant boilers work can help explain common faults and their solutions. Vaillant is an international company based in Germany, with a strong presence in Spain and more than 145 years of experience in the heating and ventilation industry. Their boilers are known for:
- Advanced technology that complies with eco-friendly design standards.
- A combination of stylish design, durability, and an intuitive user interface.
- A simple error code system displayed on the control panel, with clear explanations in the user manual.
Let’s now review a summary of common causes and solutions when a Vaillant boiler fails to heat water.
Summary Table: Why Your Vaillant Boiler Isn’t Heating Water
Below is a helpful table of common faults and their associated error codes, based on the official Vaillant manuals. After the table, we’ll go into more detail about some specific cases.
| Error Code | Issue | Solution |
| F22, F23, F24 | Safety lockout due to lack of water. The boiler may be empty, the pressure sensor may be faulty, or wiring to the pump or sensor could be loose or damaged. | Refill the system with water. Check the pressure sensor and circulation pump. Unblock or replace the pump if needed. Make sure the gravity brake is properly installed and functioning. |
| F27, F28, F29 | No gas due to various reasons, such as a faulty regulator, frozen gas tank, or partially closed valve. | Restore gas flow and check the ignition circuit. Inspect and replace the regulator if necessary. If using butane, move the tank to a warmer location or switch to propane. |
| F75 | Circulation pump failure. | Try rotating the pump shaft manually with a flat tool to unblock it. If this doesn’t work, replace the pump. |
Other Reasons Your Vaillant Boiler Might Not Heat Water
Besides the error codes listed above, there are additional issues that technicians frequently encounter. These may not always be included in the manuals but are common in day-to-day troubleshooting.
Faulty Diverter Valve (Three-Way Valve)
If your boiler seems to be working but no hot water comes out of the taps, the diverter valve could be stuck or broken. This valve controls the flow of hot water between the heating system and the domestic hot water circuit. In a combi boiler, the diverter valve directs the heated water to radiators or taps depending on demand.
Signs of a faulty diverter valve include:
- Radiators heat up even when only hot water is requested.
- Hot water flows through taps, but the heating system is not turned on.
- Radiators don’t heat up when the heating is on, but hot water is still available.
These symptoms suggest the circuits are overlapping and the hot water is flowing in the wrong direction or at the wrong time. In this case, the valve may need to be cleaned, repaired, or replaced.
Limescale Buildup in the Heat Exchanger
In boilers that provide instant hot water, the heat exchanger or coil is a key component. Positioned close to the burner, it transfers heat directly to the water. Over time, minerals and limescale can build up inside the exchanger, reducing its ability to heat water efficiently.
When this happens, users may notice that the water temperature is too low, even though the boiler seems to be working correctly. Fuel consumption might also increase, leading to higher energy bills and more emissions.
You may also hear unusual noises when the boiler is heating water. These are signs that the heat exchanger is blocked with scale. The solution is to clean and descale the coil. This process should only be done by a qualified technician, as it involves disassembling the boiler.
How the Cleaning Process Works
- Remove the heat exchanger from the boiler.
- Place it in a container with proper drainage.
- Pour hydrochloric acid (salfumán) into the coil and let it sit to dissolve the scale.
- Rinse thoroughly with clean water until the flow runs clear.
- Use a wire brush to remove any soot or debris from the outside, taking care not to damage the material.
- Reinstall the exchanger and restart the boiler.
You can learn more about this process in our guide on how to clean a gas water heater.
Importance of Annual Maintenance
Many boiler issues can be prevented with regular servicing. According to current regulations, boilers should receive at least one full maintenance check per year. This helps identify early signs of problems, such as worn-out parts, electrical faults, or dirt buildup.
Although an annual service may seem like an added cost, it often prevents more expensive repairs down the line. It also helps maintain efficiency and reduces gas consumption.
Access to Vaillant Manuals
If you need help understanding your boiler model, you can download official Vaillant manuals using the following links. These are hosted on the official Vaillant Spain website and should be available whenever you need them:
- Manuals for various Vaillant condensing boilers
- ecoTEC plus combi boiler manual
- ecoCOMPACT boiler manual
- ecoTEC plus SMART boiler manual
- ecoTEC exclusive boiler manual
Order Vaillant Spare Parts from Suner
Whether you’re ordering online or visiting one of our regional branches, Suner provides a wide selection of original Vaillant replacement parts. We also stock over 30,000 components from leading brands in the heating industry.
- Browse Vaillant parts at Suner
- Explore over 30,000 parts at Suner
As a trusted supplier, we offer:
- Fast and secure delivery of all items.
- Sales limited to certified professionals or technicians only.
- Assistance identifying the correct part based on codes or photos.
- Guaranteed delivery by 10:00 AM the next morning for orders placed before 5:30 or 6:00 PM.
If you have questions about becoming a client or placing an order, visit our FAQ section. Suner is here to support your business with reliable service and top-quality parts all year round.