Vaillant F75 Fault Code: Causes, Symptoms & Solutions
What Does the Vaillant F75 Fault Code Mean?
The Vaillant F75 fault code indicates a failure in detecting sufficient water pressure during startup.
This typically results from a faulty pump, a malfunctioning pressure sensor, or hidden leaks within the central heating system.
When the boiler initiates, the pressure sensor expects a fluctuation in pressure as the pump activates.
If no change is detected, the system halts operation and displays the F75 error to prevent damage.
Common Causes of the Vaillant F75 Fault
Several factors can trigger the Vaillant F75 fault code, including:
The F75 code commonly arises from one or more of the following system failures:
1. Faulty Pressure Sensor
The pressure sensor may fail to register water pressure changes, leading the boiler to believe the system is empty, even when pressure appears normal.
2. Pump Malfunction
If the pump is seized or malfunctioning, it cannot circulate water, which results in zero pressure variation — a direct trigger for the F75 fault.
3. Airlocks in the Heating System
Trapped air prevents proper circulation, which mimics a mechanical fault by stopping pressure changes during system startup.
4. Blockages from Debris or Sludge
Internal sludge or scale build-up can block flow to the sensor or pump, especially in older or poorly maintained systems.
Symptoms of an F75 Fault
You may notice the following signs if your boiler is experiencing an F75 error:
- 🚫 No heating or hot water
- 🛟 Red warning light on boiler display
- 🔊 Humming or clicking sounds during startup
- 🔄 Pressure gauge reads zero or remains unchanged
These are indicators of either failed internal components or water pressure-related faults, which may involve invisible system leaks.
How to Fix the Vaillant F75 Fault (DIY First Steps)
If you’re experiencing the F75 code, try the following steps before calling an engineer:
✅ Step 1: Bleed Your Radiators
Trapped air can interfere with circulation. Bleeding restores balanced water flow and pressure.
✅ Step 2: Top Up System Pressure
Use the filling loop to restore pressure to 1.5 bar. If the pressure drops again, you may have a slow leak.
✅ Step 3: Reset the Boiler
After completing the above, press the boiler’s reset button. Monitor for return of the error.
🧠 Repeated F75 faults after resets typically indicate a deeper issue like leaks, pump failure, or sensor damage.
When to Suspect a Hidden Leak
If your boiler:
- Keeps losing pressure
- Regains pressure after top-up but drops again
- Has no visible signs of leaking water
…then the issue may be a concealed leak in your central heating system.
ADI Leak Detection can trace leaks non-invasively, using:
- 🔊 Acoustic Listening Devices
- 🌡️ Thermal Imaging
- 🧪 Tracer Gas Detection
These techniques locate leaks without tearing up floors or walls.
Vaillant F75 Fault – Frequently Asked Questions
The F75 fault occurs when the boiler doesn’t detect a pressure increase, often due to a failing pump, pressure sensor, or internal blockage.
Yes — undetected water leaks reduce pressure over time. This prevents proper pressure detection, which triggers the F75 code during system checks.
The F75 fault prevents unsafe boiler operation. It’s a built-in safety mechanism, but ignoring the root cause (like a leak) can lead to system damage.
Common models include:
- ecoTEC Plus 824, 831, 837
- ecoTEC Pro 24, 28
- turboTEC Pro/Plus series
Yes. Airlocks stop water circulation, which prevents the pressure sensor from detecting pressure changes, causing the error code.
Signs include:
- Lack of vibration or noise from the pump
- Cold radiators despite the boiler running
Repeated F75 codes despite normal pressure
Engineers often replace the sensor first, as it’s cheaper. If the fault remains, the pump may be at fault and require replacement.
- Annual boiler servicing
- Installing a magnetic system filter
- Adding corrosion inhibitor
- Prompt leak detection when pressure loss occurs
Call ADI Leak Detection – Trusted F75 & Leak Detection Experts
If you’ve:
- Repeatedly reset the boiler
- Topped up pressure but still see F75
- Found no visible leak, but still lose pressure…
Then it’s time to call ADI Leak Detection.
We use industry-leading equipment to locate hidden leaks with:
- No floor lifting
- No drywall damage
- No unnecessary part replacements
Call 0800 731 3843 today or book online to resolve your F75 boiler issue quickly and non-invasively.
