F.75
Vaillant Boiler
Severity: ModerateWhat Does This Error Mean?
F.75 means low system pressure or water flow detected by the pump and pressure sensor. Most cases are resolved by repressurising the system — restoring pressure to 1.0–1.5 bar.
Affected Models
- Vaillant ecoTEC Pro
- Vaillant ecoTEC Plus
- Vaillant ecoFIT
Common Causes
- System pressure dropped below 0.8 bar (most common — repressurise)
- Air locked in the central heating system
- Faulty water pressure sensor
- Failed central heating pump
- External expansion vessel needs recharging
How to Fix It
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Check the pressure gauge.
The boiler pressure gauge should read 1.0–1.5 bar when cold. If below 0.8, the system is undercharged and F.75 will appear. If at 1.0+ bar, the issue is sensor or pump — call an engineer.
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Repressurise the system.
Locate the filling loop (a flexible silver hose under the boiler). Open both filling loop valves slowly until the pressure gauge reads 1.0–1.5 bar. Close both valves firmly. Reset the boiler.
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Bleed the radiators.
If the system pressure drops only when heating starts, there is air trapped. Bleed each radiator with a bleed key until water comes out. Check pressure after bleeding and top up if needed.
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Look for system leaks.
If pressure drops repeatedly to F.75, there is a leak somewhere in the system. Check radiator valves, pipework joints, and around the boiler. A persistent leak needs an engineer to find and repair.
When to Call a Professional
Repressurising is a user task. If the pressure drops repeatedly after refilling, the system has a leak somewhere — find and fix the leak with a heating engineer's help. Pressure sensor and pump replacements require a Gas Safe engineer.