What does the Vaillant F75 error code mean?
F75 is a long-standing Vaillant ecoTEC complaint. When the pump starts, the boiler expects a small pressure rise; if it doesn't see one, it locks out with F75. It's usually a worn pressure sensor, a weak pump, or a pinhole leak bleeding pressure.
What causes the Vaillant F75 fault?
The F75 error on a Vaillant boiler is most commonly triggered by:
- A worn or scaled differential pressure sensor
- A weak or failing central heating pump
- A pinhole leak in the heat exchanger or pipework dropping pressure
- Air in the pump preventing it from producing the expected pressure rise
How to fix the Vaillant F75 boiler fault
Follow these steps. If the code returns after you have completed them, stop and call a Gas Safe engineer.
- 1.Confirm system pressure is at 1.0–1.5 bar and top up if needed — low pressure can trigger F75 alongside pump/sensor faults.
- 2.Book an engineer: replacing the pressure sensor is the most common fix; if that doesn't resolve it, the pump or heat exchanger needs inspecting.
Frequently asked questions about the Vaillant F75
What does F75 mean on a Vaillant ecoTEC?
F75 means the boiler didn't see the expected pressure rise when the pump started. It's usually a faulty pressure sensor, occasionally a weak pump or an internal leak.
Is the Vaillant F75 fault serious?
It stops the boiler firing, so it needs an engineer, but it's very common and usually fixed by replacing the pressure sensor — a straightforward job for a Gas Safe engineer.