Vaillant & Saunier Duval Boiler Error F22 (F.22): Causes, How to Repressurise & Fix
You step into the shower expecting hot water and get hit by an icy blast instead. Checking your Vaillant (ecoTEC, turboTEC) or Saunier Duval (Thema, Isofast) boiler, you see a flashing red light and code F22 or F.22. This safety lockout means low water pressure or dry-fire protection in the primary heating circuit. In 70% of cases you can restore hot water yourself in two minutes—here is how.
What Does Error Code F22 (F.22) Mean?
Modern condensing boilers use an electronic water pressure sensor to prevent the burner from firing without water, which would melt the heat exchanger in seconds.
Whenever internal pressure drops below 0.5 bar (or the PCB detects no water circulation), the boiler immediately locks out with code F22.
Step-by-Step: How to Top Up Boiler Pressure with the Filling Loop
1. Look underneath the boiler to locate the filling tap (llave de llenado). On Saunier Duval boilers it is usually a blue lever or knob; on Vaillant boilers it is a grey/metallic tap or slotted screw.
2. Turn the filling valve slowly anti-clockwise. You will hear water flowing into the sealed heating circuit.
3. Watch the pressure gauge or digital display until it reads between 1.2 and 1.5 bar (when the heating is cold).
4. Close the filling valve firmly. Leaving it slightly open will cause pressure to exceed 3 bar, triggering the pressure relief valve to discharge water.
5. Most boilers restart automatically at 1.2 bar. If F22 remains on screen, press and hold the Reset button (crossed-out flame icon) for 3 seconds.
What If the Gauge Reads 1.5 Bar and Error F22 Still Shows?
If the analogue gauge shows 1.5 bar while the digital screen stays locked on F22, or if turning the blue tap does nothing, one of three internal components has failed:
1. Blocked electronic pressure sensor: magnetite sludge or limescale blocks the sensor's tiny pinhole, sending a false 0.0 bar reading to the main board.
2. Seized circulation pump: if the pump rotor is jammed, the boiler triggers F22 due to lack of circulation.
3. Flat expansion vessel or hidden leak: if you have to top up water every 24–48 hours, the expansion vessel has lost its nitrogen charge or a radiator pipe is leaking.
Our 24/7 emergency boiler engineers in Barcelona, Sabadell, Terrassa and Girona carry genuine Vaillant and Saunier Duval pressure sensors, filling valves and pumps. Call 936 94 00 23 (+34 936 94 00 23).
FAQ
What is the normal water pressure for a Vaillant or Saunier Duval boiler?
When the radiators are cold, boiler pressure should sit between 1.2 and 1.5 bar. When the heating is running hot, it normally rises to 1.8–2.0 bar.
What if I overfilled the boiler past 2.5 bar?
Close the filling tap completely and bleed a radiator into a cup or bowl until the boiler pressure gauge drops back to 1.5 bar.