- Boilers
- Gas boiler
F53
Saunier Duval F.53 on a gas boiler: Venturi flow sensor fault
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Saunier Duval F.53 means a fault in the Venturi flow sensor; the first listed cause is low gas pressure. Check that the gas valve is open and press reset once. If it comes back, call the official service centre.
Safety first
Stop and check this first
- If you smell fumes indoors: Saunier Duval says to open doors and windows fully, switch the appliance off and call a professional. Poor combustion or fumes that do not clear properly can fill the home with carbon monoxide, which has no smell: if you feel headache, dizziness or nausea, ventilate, get out and call for help. A CO alarm helps.
- 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, warn neighbours without the bell, leave the building and call the gas company from a phone outside.
- Do not open the boiler to check connectors or cables: Saunier Duval tells you never to do maintenance or repair work yourself and to leave it to a qualified installer. Inside there is mains voltage and gas parts.
Safe checks you can perform
- Gas isolation valve
- Code on the display and other codes
- Recent work on the boiler
- One reset with the fault key
- Gas pressure, Venturi and sensor checked by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Gas connection pressure at full load
- Do not attempt this professional task: Venturi tube filter and test point
- Do not attempt this professional task: Combustion analysis after the repair
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.
Gas connection pressure at full load
What they doThe technician measures the gas connection pressure with a manometer with the boiler at full load, as the Saunier Duval service routine requires.
They must show youthe measured pressure against the manufacturer's specification.
In writingthe value and what was corrected in the supply.
Venturi tube filter and test point
What they doChecks the Venturi filter cap filter and the internal pressure test point, without using lubricants on the O ring.
They must show youthe condition of the filter and the test point.
In writingwhat was found and what was cleaned or replaced.
Combustion analysis after the repair
What they doConnects an analyser to the flue gas test point, runs the boiler at full load with test programme P.01 at 100, waits for a stable reading and measures CO2.
They must show youthe measured CO2 against the manufacturer's table for your gas type.
In writingthe value and the test run.
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.
Gas isolation valve
- Who:
- you.
- How:
- check that the boiler gas isolation valve and the building one are open, as Saunier Duval asks. Do not touch any other part.
- Result that matters:
- whether a valve was closed or half closed.
- If it was closed or half closed:
- open it fully and go on to the reset.
- If they were open:
- the valve is ruled out; the gas pressure behind F.53 is measured by the technician.
- Evidence to keep:
- a photo of the valve position.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Code on the display and other codes
- Who:
- you.
- How:
- take a photo of the display. If several faults are present, Saunier Duval shows them alternately every two seconds: wait a few seconds and note them all.
- Result that matters:
- whether F.53 appears alone or alternates with other codes.
- If it appears alone:
- the fault is in what F.53 monitors; go on to the next check.
- If it alternates with others:
- note them all; if F.52 appears, the sensor is disconnected, and the technician needs to know.
- Evidence to keep:
- photos of the display with date and time.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Recent work on the boiler
- Who:
- you.
- How:
- think back to whether anyone opened the boiler recently for a service or a repair.
- Result that matters:
- whether F.53 started right after it.
- If it started after some work:
- tell the technician; Saunier Duval says not to lubricate the Venturi O ring and a blocked test point is one of the causes.
- If there was no work:
- gas pressure, filter or sensor may be the cause; the technician separates them by measuring.
- Evidence to keep:
- date and report of the last service.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00 · Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
One reset with the fault key
- Who:
- you.
- How:
- press the fault clearing (reset) key and wait five seconds, as Saunier Duval describes. Do it once only.
- Result that matters:
- whether F.53 comes back.
- If it clears and stays away:
- note the date and tell the technician at the next service.
- If it persists or returns:
- do not keep resetting; call the official service centre.
- Evidence to keep:
- a photo of the display with the code and the time.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Gas pressure, Venturi and sensor checked by the technician
- Who:
- official service centre technician or qualified installer.
- How:
- measures the gas connection pressure at full load, checks the Venturi filter cap filter and its internal pressure test point, and tests the volumetric sensor.
- Result that matters:
- which of the four Saunier Duval causes is present.
- If gas pressure is outside its specification:
- the supply is corrected before touching the boiler.
- If the pressure is fine:
- the filter, test point or sensor is cleaned or replaced as found.
- Evidence to keep:
- a report with the measured gas pressure and what was cleaned or replaced.
The gas valve, the flame and the flue are gas and combustion parts. Saunier Duval reserves this work for a qualified installer: do not open the casing.
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
- anomalía F53 Miele
- anomalía F53 secadora Miele
- anomalie F53 Miele
- code erreur F53 lave-vaisselle Miele
- error F53 lavavajillas Miele
- Error F53 Saunier Duval
- errore F53 lavastoviglie Miele
- F.53
- Fehlercode F53 Miele
- guasto F53 Miele
- Miele dishwasher F53
- Miele dryer F53
- Miele dryer F53 drive motor
- Miele F53
- Miele F53 fault tumble dryer
- Miele F53 secadora
- Miele fault F53
- Miele Geschirrspüler Fehler F53
- Saunier Duval F.53
- secadora Miele F53 motor
- ThemaFast Condens F.53
What it means
In the ThemaFast Condens table, F.53 is circulating flow sensor fault. Saunier Duval gives four causes: insufficient gas flow pressure, the filter in the Venturi tube filter cap wet or blocked, a faulty volumetric sensor and the internal pressure test point in the Venturi tube blocked. The manufacturer warns not to use lubricants on the Venturi tube O ring. If the sensor is disconnected the code is a different one, F.52. The code does not say which of the four causes is acting.
Warnings and stop conditions
- Higheditorial warning
If you smell fumes indoors: Saunier Duval says to open doors and windows fully, switch the appliance off and call a professional. Poor combustion or fumes that do not clear properly can fill the home with carbon monoxide, which has no smell: if you feel headache, dizziness or nausea, ventilate, get out and call for help. A CO alarm helps.
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, warn neighbours without the bell, leave the building and call the gas company from a phone outside.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
- Mediumsource verified
Do not open the boiler to check connectors or cables: Saunier Duval tells you never to do maintenance or repair work yourself and to leave it to a qualified installer. Inside there is mains voltage and gas parts.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Symptoms and causes
Probable causes · in order
- Insufficient gas flow pressurePossible
It is the first cause in the table. It fits if the gas valve was not fully open. The technician measures the gas connection pressure at full load.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00 · Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
- Venturi tube filter wet or blockedPossible
The filter in the Venturi filter cap can get wet or clogged. Only the technician checks it, with the boiler open and powered off.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Venturi pressure test point blockedPossible
Saunier Duval warns not to lubricate the Venturi tube O ring. This point is worth checking if F.53 started right after a service.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Faulty volumetric sensorPossible
If gas pressure, filter and test point are fine, the sensor itself remains. The technician rules out the rest before replacing it.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
Virtual technician
Does F53 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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