
Among all the error codes that can appear on Vaillant boilers, F4 is one of the most common. This code (often written as F.4 in manuals) signals an issue with gas pressure. It’s a technical fault that must be handled by a qualified technician. If a simple reset doesn’t clear the error, users should not try to fix it on their own.
It’s also important to note that error code F4 is used by several other boiler brands—including Saunier Duval, Viessmann, Fagor, and Ariston—to indicate flame or ignition failures. This can lead to confusion when searching for solutions online. In this article, we’ll focus specifically on F4 errors in Vaillant boilers, which are typically related to gas pressure or valve issues.
Later in the article, we’ll also cover the F.04 error, which shows up in Vaillant water heaters and refers to a similar ignition fault.
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At Suner, we stock a wide range of official Vaillant replacement parts. You can browse all available Vaillant products through the first link below. If you’re looking for parts specific to a boiler model, follow the second link, use our advanced search tool, and select your boiler model from the dropdown menu to view compatible parts.
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Causes and Solutions for the F4 Error in Vaillant Boilers
As explained earlier, the F4 error in a Vaillant boiler indicates a gas pressure issue. This can happen for a variety of reasons. Here’s a complete breakdown of potential causes and what to do in each case:
Problem | Solution |
The gas valve is closed or faulty. | First, check whether the gas valve is unintentionally closed and open it if needed. If the valve is defective, it must be replaced. |
Blockages or gas leaks in the supply line. | Inspect the installation for blockages or leaks and address them immediately, especially in case of gas leaks. |
Air has entered the gas line, affecting pressure. | Bleed the gas installation to remove the air. |
Faulty or incorrect gas regulator. | Different gas types require specific regulators. If the regulator is broken or not suitable, it needs to be replaced with the correct one. |
The gas bottle doesn’t release gas due to freezing. | This usually happens with butane, not propane. In colder regions, switching from butane to propane is the best solution. |
Notes on Low Temperatures and Gas Bottles
In cold climates, butane gas bottles can stop working during freezing conditions. Contrary to popular belief, this isn’t because the gas inside freezes. Instead, the pressure difference between the inside and outside of the bottle prevents the gas from flowing out. The fix is simple: switch to propane, which continues to flow normally even in freezing temperatures.
What About Error F.04 in Vaillant Water Heaters?
As mentioned earlier, the F4 error also appears in Vaillant water heaters but is labeled as F.04. It refers to an ignition failure. This fault occurs when the burner fails to ignite or lights briefly before shutting off again. While the cause is similar to the F4 boiler error, in water heaters it’s slightly broader and more focused on burner performance.