- Boilers
- Gas boiler
F75
Saunier Duval F75 boiler: pressure sensor or pump fault
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Fault code F75 (shown as F.75) on a Saunier Duval Thelia Condens or Semia Condens boiler indicates a water pressure sensor error, a defective circulation pump, or a lack of water in the system. Check that cold pressure is between 1.0 bar and 1.5 bar, try at most one reset, and call an engineer.
Safety first
Stop and check this first
- Do not remove the front panel or attempt to unclip the pressure sensor, clean the internal heating filter, or dismantle the 230 V pump head yourself; all internal hydraulic and electrical work must be performed by a qualified installer.
- If you smell gas inside the building, open all doors and windows wide, avoid naked flames, do not operate electrical switches, sockets, doorbells, or telephones, close the main gas shut-off valve if safe, leave the building immediately, and call the gas emergency service from outside.
Safe checks you can perform
- Check system pressure on the display and top up to 1.0 - 1.5 bar if low
- Ensure radiator valves are open and bleed trapped air from radiators
- Attempt one single reset by holding the reset key for more than 3 seconds
Leave these tasks to a qualified professional
- Do not attempt this professional task: Test internal pump operation (d.10, d.15), clean heating filter, and run purge P.06
- Do not attempt this professional task: Inspect or replace the water pressure sensor and check expansion vessel pre-charge
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.
Test internal pump operation (d.10, d.15), clean heating filter, and run purge P.06
What they doCheck internal pump status and speed via diagnostic codes d.10 and d.15, ensure the automatic air vent cap on the internal pump is open, clean the heating filter (section 11.13), run heating circuit purge programme P.06, and replace the pump head (section 12.6.5) if defective.
They must show youDiagnostic readings in d.10 and d.15, the cleaned heating filter, and the old pump head if replaced.
In writingPump diagnostic values (d.10, d.15), heating filter cleaning confirmation, and purge programme P.06 result.
Inspect or replace the water pressure sensor and check expansion vessel pre-charge
What they doDrain the boiler using test programme P.05, remove and inspect the water pressure sensor (section 12.6.11) replacing it if faulty, and measure expansion vessel pre-charge pressure (section 11.16, recharging if below 0.075 MPa / 0.75 bar).
They must show youThe removed water pressure sensor and the pressure gauge reading at the expansion vessel valve.
In writingReplacement pressure sensor part reference, expansion vessel pre-charge reading in bar, and final system fill pressure.
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.
Check system pressure on the display and top up to 1.0 - 1.5 bar if low
- Who:
- you, using the display buttons and the filling valve.
- How:
- Verify that system pressure on the display is between 0.1 MPa and 0.15 MPa (1.0 bar and 1.5 bar); if flow temperature is shown instead, hold the minus and plus keys simultaneously for more than 5 seconds to view pressure. If low, open all radiator thermostatic valves, slowly open the filling valve underneath until pressure reaches 1.0 bar to 1.5 bar, then close the valve tightly.
- Result that matters:
- Restores adequate water volume before suspecting a failed pump or pressure sensor.
- If pressure was below 1.0 bar, top it up to between 1.0 bar and 1.5 bar and make sure the filling tap is fully closed.
- If pressure is already between 1.0 bar and 1.5 bar, do not add extra water; move to the next check.
- Evidence to keep:
- Photo of the bar pressure reading on the boiler display.
Evidence: Saunier Duval Thelia Condens y Semia Condens, instrucciones de funcionamiento 0020199012_04
Ensure radiator valves are open and bleed trapped air from radiators
- Who:
- you, at the radiators in your home.
- How:
- Confirm that radiator thermostatic valves are open and, if there is air in the heating system, bleed the radiators while cold and re-check that boiler pressure remains between 1.0 bar and 1.5 bar.
- Result that matters:
- Clears air pockets that stop the circulation pump from generating a pressure pulse.
- If air escaped when bleeding the radiators, top the system back up to 1.0 bar to 1.5 bar afterwards.
- If no air was present or pressure drops repeatedly, note this down for the attending engineer.
- Evidence to keep:
- Note recording whether radiators were bled and the resulting system pressure.
Evidence: Saunier Duval Thelia Condens y Semia Condens, instrucciones de funcionamiento 0020199012_04
Attempt one single reset by holding the reset key for more than 3 seconds
- Who:
- you, pressing the reset button once on the control panel.
- How:
- Once cold system pressure is between 1.0 bar and 1.5 bar, hold the reset key down for more than 3 seconds once and watch whether F.75 clears from the screen.
- Result that matters:
- Tests whether restoring water pressure and bleeding air resolved the fault.
- If F.75 clears and the boiler runs quietly, monitor the pressure reading over the following days.
- If F.75 reappears after that single reset attempt, do not repeat resets; contact an authorised Saunier Duval service engineer.
- Evidence to keep:
- Timestamp of the single reset attempt and the code displayed afterwards.
Evidence: Saunier Duval Thelia Condens y Semia Condens, instrucciones de instalación y mantenimiento 0020199140_05 · Saunier Duval Thelia Condens y Semia Condens, instrucciones de funcionamiento 0020199012_04
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
- 75
- caldera Saunier Duval F.75
- code erreur F75 chaudière Vaillant
- codice F75 Vaillant
- error F75 Saunier Duval
- Error F75 Vaillant
- errore F75 caldaia Vaillant
- F 75
- Fehlercode F75 Vaillant
- Glow worm boiler F75
- Glow worm F75
- Glow-worm F.75
- Glow-worm F75
- Glow-worm F75 pump pressure
- panne F75 Vaillant
- Saunier Duval F75
- Saunier Duval fault code F.75
- Semia Condens F75
- Thelia Condens F75
- Vaillant F.75
- Vaillant F75
- Vaillant F75 fault
- Vaillant Fehler F75
What it means
On Saunier Duval Thelia Condens and Semia Condens condensing boilers (whose official product manuals for the Spanish market are in Spanish), fault code F.75 means the control board did not detect the expected pressure response when starting the pump, listed officially as a defective pressure sensor or pump, or lack of water. The code alone never proves the pump or pressure sensor has failed, because low system water pressure, trapped air, or a blocked heating filter can prevent the pressure change.
Warnings and stop conditions
- Highsource verified
Do not remove the front panel or attempt to unclip the pressure sensor, clean the internal heating filter, or dismantle the 230 V pump head yourself; all internal hydraulic and electrical work must be performed by a qualified installer.
Evidence: Saunier Duval Thelia Condens y Semia Condens, instrucciones de instalación y mantenimiento 0020199140_05 · Saunier Duval Thelia Condens y Semia Condens, instrucciones de funcionamiento 0020199012_04
- Highsource verified
If you smell gas inside the building, open all doors and windows wide, avoid naked flames, do not operate electrical switches, sockets, doorbells, or telephones, close the main gas shut-off valve if safe, leave the building immediately, and call the gas emergency service from outside.
Evidence: Saunier Duval Thelia Condens y Semia Condens, instrucciones de funcionamiento 0020199012_04
Symptoms and causes
Probable causes · in order
- Lack of water or low pressure in the central heating systemCommon
Cold filling pressure has dropped below the required 0.1 MPa to 0.15 MPa (1.0 bar to 1.5 bar) range, or air pockets in the circuit prevent the pump from building pressure.
Evidence: Saunier Duval Thelia Condens y Semia Condens, instrucciones de instalación y mantenimiento 0020199140_05 · Saunier Duval Thelia Condens y Semia Condens, instrucciones de funcionamiento 0020199012_04
- Defective or blocked water pressure sensorCommon
System debris or magnetite sludge is blocking the sensing port of the water pressure transducer, or the sensor itself has failed electrically.
Evidence: Saunier Duval Thelia Condens y Semia Condens, instrucciones de instalación y mantenimiento 0020199140_05
- Seized, air-locked, or faulty internal heating circulation pumpPossible
The internal pump head is jammed, air-locked because its automatic air vent cap is shut, or electrically faulty and unable to circulate water.
Evidence: Saunier Duval Thelia Condens y Semia Condens, instrucciones de instalación y mantenimiento 0020199140_05
Virtual technician
Does F75 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 · 2018 · manual
- 2
Saunier Duval Thelia Condens y Semia Condens, instrucciones de funcionamiento 0020199012_04
Saunier Duval · 2016 · manual
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