- Boilers
- Gas boiler
F00
Saunier Duval F.00 on a gas boiler: flow sensor open circuit
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Saunier Duval F.00 means an open circuit in the flow temperature sensor: the board gets no signal from it. Take a photo of the code, press the reset key once and wait five seconds. If it stays, call the official service centre.
Safety first
Stop and check this first
- 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.
- 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.
Safe checks you can perform
- Code on the display and other codes
- Recent work on the boiler
- One reset with the fault key
- Connectors, harness and sensor checked by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Sensor and board connectors
- Do not attempt this professional task: Harness continuity and sensor resistance
- Do not attempt this professional task: Flow reading and fault memory
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.
Sensor and board connectors
What they doWith the boiler disconnected from power, the technician checks the flow NTC sensor connector and the circuit board multi connector.
They must show youphotos of the connectors before and after.
In writingwhich connector was loose or that they were fine.
Harness continuity and sensor resistance
What they doMeasures with a multimeter the cable continuity between sensor and board and the resistance of the flow NTC sensor.
They must show youthe measured value against the manufacturer's specification.
In writingthe value, any part replaced, its reference and why.
Flow reading and fault memory
What they doAfter the repair, reads the last 10 codes in the fault memory and checks the flow temperature on diagnostic code d.40 with the boiler running.
They must show youthe list of codes and the d.40 reading.
In writingthe codes found before clearing them and the operating test.
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.
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.00 appears alone or alternates with other codes.
- If it appears alone:
- the fault is in what F.00 monitors; go on to the next check.
- If it alternates with others:
- note them all; the technician needs them for the diagnosis.
- 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.00 started right after it.
- If it started after some work:
- tell the technician; a loose connector is the first cause Saunier Duval gives.
- If there was no work:
- the part or its cable may have failed on its own; 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.00 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
Connectors, harness and sensor checked by the technician
- Who:
- official service centre technician or qualified installer.
- How:
- with the boiler disconnected from power, checks the flow sensor connector, the board multi connector and the wiring harness, and measures the NTC sensor.
- Result that matters:
- where the open circuit is.
- If a connector was loose or the cable cut:
- that was the cause; the sensor does not need replacing.
- If connectors and cable are fine and the sensor does not give a correct value:
- the sensor is replaced.
- Evidence to keep:
- a report with what was measured and replaced.
Saunier Duval reserves inspection, maintenance, repair and gas adjustments 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
- ecoTEC F.00
- Error F00 Saunier Duval
- Error F00 Vaillant
- F.0
- F.00
- Saunier Duval F.00
- ThemaFast Condens F.00
- Vaillant F.00
What it means
In the ThemaFast Condens table, F.00 is open circuit in the flow temperature sensor, the NTC sensor on the heating flow. Saunier Duval gives four causes: NTC connector loose or not plugged in, circuit board multi connector badly inserted, a break in the wiring harness or a faulty NTC sensor. If the sensor is short circuited the code is a different one, F.10. Without the flow reading the board cannot control the burner. The code does not say which of these parts has failed.
Warnings and stop conditions
- 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
- 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
Symptoms and causes
Probable causes · in order
- NTC connector loose or not plugged inPossible
Saunier Duval lists it first. It fits if F.00 started right after a service or repair with the boiler opened.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Circuit board multi connector badly insertedPossible
The same open circuit, but at the board end. The technician tells them apart by checking that connector before touching the sensor.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Break in the wiring harnessPossible
A cut cable gives the same code as a broken sensor. It is separated by measuring cable continuity between sensor and board.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
- Faulty NTC flow sensorPossible
If connectors and cable are fine, the sensor itself may be open. It is confirmed by measuring its resistance against the manufacturer's specification.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
Virtual technician
Does F00 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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