What to check, in order
- Check the pressure gauge
Vaillant lists low system pressure and too little water among the causes. With the system cold, its ecoTEC plus manual wants 1.0 to 2.0 bar.
- Top up if it's low
Open the filling loop slowly until the gauge reaches the right pressure, then close it again.
When to call a Gas Safe engineer
If the pressure is fine, or F75 comes back, call a Gas Safe registered engineer. Vaillant lists a faulty pressure sensor, pump or internal expansion vessel, air in the boiler and wiring faults.
A repair visit will usually check the pressure sensor, the pump, the expansion vessel and the pressure relief valve.
- Note the model and serial number. They're on a label on the data badge, usually under the boiler or behind the front cover.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Vaillant F75 fault code mean?
When the boiler's pump started, the pressure didn't change as much as it should. Low system pressure, the pump or the pressure sensor can cause it.
Can I fix Vaillant F75 myself?
Engineer only (10 minutes of checks). Start with: check the pressure gauge; top up if it's low. If the pressure is fine, or F75 comes back, call a Gas Safe registered engineer. Vaillant lists a faulty pressure sensor, pump or internal expansion vessel, air in the boiler and wiring faults.
Is Vaillant F75 worth repairing?
Get a quote first. If the pressure was fine, the fault is a part inside the boiler, such as the pump or the pressure sensor, so ask for a price first.
Checked against
- Vaillant: boiler fault codes list
- Vaillant ecoTEC plus VU, VUW, VUI ..6/5-5 operating instructions (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.