- Boilers
- Gas boiler
F75
Vaillant boiler F75: the pressure sensor did not detect the expected change when the pump started
Evidence linked to this decision
View source: Vaillant UK boiler fault codesRisk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
F75 means the pressure sensor did not detect the expected change when the pump started in the cited model family. Do not buy a part from the display. First record the cold gauge reading and whether it changes at all when a normal heat request starts; do not remove the casing. A stable gauge does not identify the part: the engineer must separate no pump movement from a sensor that cannot report it.
Safety first
Stop and check this first
- Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Safe checks you can perform
- Capture the failure pattern before clearing it
- Run the safe discriminating check
- Use recurrence as the decision point
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measured service test for F75
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.
Measured service test for F75
What they doMeasure pump command/current and compare the pressure-sensor response with a calibrated gauge.
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.
Capture the failure pattern before clearing it
Photograph F75, both exact model identifiers and the operating state. Record the cold gauge reading and whether it changes at all when a normal heat request starts; do not remove the casing.
Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Evidence: Vaillant UK boiler fault codes list
Run the safe discriminating check
Stay outside sealed or powered compartments. A stable gauge does not identify the part: the engineer must separate no pump movement from a sensor that cannot report it. If the observation is unclear, stop and treat the internal branch as unresolved.
Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Evidence: Vaillant UK boiler fault codes list
Use recurrence as the decision point
Only if the exact user manual permits it and no stop condition exists, make one controlled attempt. If F75 returns, stop; repeated resets destroy evidence and can worsen the fault.
Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Evidence: Vaillant UK boiler fault codes list
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Virtual technician
Does F75 still appear after these checks?
This guided flow uses the exact code and your answers to choose a test, an expected result and the next branch.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Vaillant
- 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
Vaillant's official regional documentation associates F75 with the pressure sensor did not detect the expected change when the pump started. That is the controller's observed condition, not a universal failed component. Confirm the exact model before using this decision path; the same code can mean something else on another product family.
Warnings and stop conditions
- Highsource verified
Gas smell, a CO alarm, smoke, symptoms, escaping hot water or abnormal combustion means no reset: leave if safe and call the local gas emergency service from outside. Never open the boiler casing.
Evidence: Vaillant UK boiler fault codes list
Symptoms and causes
Probable causes · in order
- First branch to separate: no hydraulic pressure response when the pump startsPossible
The documented condition is the pressure sensor did not detect the expected change when the pump started. Discriminating observation: Record the cold gauge reading and whether it changes at all when a normal heat request starts; do not remove the casing. Expected reading and decision: A stable gauge does not identify the part: the engineer must separate no pump movement from a sensor that cannot report it.
Evidence: Vaillant UK boiler fault codes list
- If that branch is ruled out: pump, sensor, expansion vessel or blocked hydraulic pathPossible
pump, sensor, expansion vessel or blocked hydraulic path remains possible only after the safe observation is recorded. The next evidence is measured, not another reset: Measure pump command/current and compare the pressure-sensor response with a calibrated gauge.
Evidence: Vaillant UK boiler fault codes list
Sources and technical references
- 1
Vaillant UK boiler fault codes
Vaillant UK · official_doc
- 2
Vaillant ecoTEC installation and maintenance instructions 0020193966_04
Vaillant UK · 2020 · manual
- 3
Health and Safety Executive · official_doc
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