- Boilers
- Gas boiler
F22
Saunier Duval F.22 on a gas boiler: low water safety shutdown
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Saunier Duval F.22 is a safety shutdown for lack of water. Check the pressure on the display: Saunier Duval recommends 1 to 1.5 bar. If it is low, top up with the filling valve; if it drops again, call the official service centre.
Safety first
Stop and check this first
- Top up with water suitable for heating and close the filling valve afterwards. Saunier Duval warns that very hard water or chemicals damage the appliance.
- If you smell gas: Saunier Duval says to keep away from the area, open doors and windows, light no flames and do not smoke, do not touch switches, sockets, doorbells or phones, close the meter and appliance gas valves, leave the building and call the gas company from a phone outside.
Safe checks you can perform
- Pressure on the display
- Top up with the filling valve
- Water under the boiler
- Sensor and wiring check by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Real pressure against the display
- Do not attempt this professional task: Leak search and expansion vessel
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Real pressure against the display
What they doThe technician measures circuit pressure with a gauge and compares it with what the boiler shows.
They must show youboth pressures.
In writingthe result and any part replaced.
Leak search and expansion vessel
What they doThe technician checks whether the circuit loses water and the expansion vessel pre charge, as Saunier Duval's maintenance asks.
They must show youthe vessel pressure and the loss test.
In writingwhere water was lost and what was repaired.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Pressure on the display
- Who:
- you.
- How:
- look at the boiler's pressure indicator with the system cold. Saunier Duval recommends 1 to 1.5 bar.
- Result that matters:
- whether it flashes below 0.5 bar.
- If it is low:
- top up as in the next check.
- If it is correct and F.22 stays:
- do not top up; call the official service centre.
- Evidence to keep:
- a photo of the display with the pressure.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Top up with the filling valve
- Who:
- you.
- How:
- open the radiator valves, slowly open the filling valve under the boiler as the professional showed you, add water to 1 to 1.5 bar and close the valve.
- Result that matters:
- whether F.22 clears and pressure holds.
- If it holds:
- it was lack of water; note the date.
- If it drops again:
- there is a leak; tell the official service centre.
- Evidence to keep:
- photos of the pressure before and after and the date of each top up.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Water under the boiler
- Who:
- you.
- How:
- look for water under the boiler or at radiators and valves.
- Result that matters:
- whether there is a visible leak.
- If there is water:
- Saunier Duval says to shut off the cold water to the appliance and tell the official service centre.
- If it is dry:
- the leak is hidden; tell the technician if pressure drops.
- Evidence to keep:
- photos of the area.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Sensor and wiring check by the technician
- Who:
- official service centre technician.
- How:
- checks real pressure, the pressure sensor and the cables to the pump and sensor.
- Result that matters:
- whether water is missing or the measurement fails.
- If the sensor fails:
- it is replaced.
- If water is missing:
- the leak is traced.
- Evidence to keep:
- a report of what was measured and repaired.
Saunier Duval reserves inspection, maintenance, repair and gas settings for a specialist installer: do not open the boiler.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Saunier Duval
- Product type
- Gas boiler
Known code variants
- 22
- code erreur F22 chaudière Vaillant
- codice F22 Vaillant
- código F22 Vaillant
- error F22 caldera Vaillant
- Error F22 Saunier Duval
- errore F22 caldaia Vaillant
- F 22
- Fehlercode F22 Vaillant
- Glow worm boiler F22
- Glow worm F22
- Glow-worm F.22
- Glow-worm F22
- Glow-worm F9 older boilers
- panne F22 Vaillant
- Saunier Duval F.22
- ThemaFast Condens F.22
- Vaillant boiler F22
- Vaillant F.22
- Vaillant F22
- Vaillant Fehler F22
What it means
In the ThemaFast Condens table, F.22 is safety shutdown: lack of water. Saunier Duval gives little or no water in the appliance, a faulty water pressure sensor, or the cable to the pump or pressure sensor disconnected or faulty as causes. In the operating instructions, with the pressure indicator flashing below 0.5 bar, the remedy is to add treated water. The code does not say whether water is really missing or the sensor or its cable fails.
Warnings and stop conditions
- Mediumsource verified
Top up with water suitable for heating and close the filling valve afterwards. Saunier Duval warns that very hard water or chemicals damage the appliance.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
- Criticalsource verified
If you smell gas: Saunier Duval says to keep away from the area, open doors and windows, light no flames and do not smoke, do not touch switches, sockets, doorbells or phones, close the meter and appliance gas valves, leave the building and call the gas company from a phone outside.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Symptoms and causes
Probable causes · in order
- Lack of water in the systemCommon
If the display shows under 0.5 bar and F.22 clears after topping up and pressure holds, this was the cause.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00 · Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
- Repeated water lossPossible
If you have to top up often, water is escaping somewhere; Saunier Duval says to call the service centre if it repeats.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
- Pressure sensor or its cablePossible
If pressure is correct and F.22 stays, Saunier Duval points to a faulty pressure sensor or its cable or the pump cable.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
Virtual technician
Does F22 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
Saunier Duval · 2016 · manual
- 2
Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Saunier Duval · 2016 · manual
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