F73On Vaillant boilers, fault code F.73 means: Water level (pressure) sensor fault. The boiler has locked out for safety. Try the safe checks below and one reset; if the code returns, call a qualified gas engineer.
Can I keep using the boiler?
The boiler has locked out for safety. Try the safe checks below and one reset; if the code returns, call a qualified gas engineer.
Common causes
- Faulty sensor or component
- Water leak in the heating system or pressure not topped up
- Damaged wiring or a loose/corroded connector
How to fix it
- Top up the pressure to about 1–1.5 bar with the filling loop or tap (see your manual)
- Have a qualified gas engineer inspect the boiler; never open gas or flue parts yourself
Frequently asked questions
What does Vaillant error F.73 mean?
On Vaillant boilers, fault code F.73 means: Water level (pressure) sensor fault.
How do I fix Vaillant error F.73?
Start with these steps: Top up the pressure to about 1–1.5 bar with the filling loop or tap (see your manual); Have a qualified gas engineer inspect the boiler; never open gas or flue parts yourself.
Is it safe to use the boiler with fault F.73?
Severity: Medium. The boiler has locked out for safety. Try the safe checks below and one reset; if the code returns, call a qualified gas engineer.