- Boilers
- Tankless gas water heater
F01
Saunier Duval F01 on gas water heater: water above 85 °C
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
F01 (or F.01) on Saunier Duval Opalia F LR gas water heaters signals overheating: the NTC probe detected water temperature above 85 °C and shut off the gas supply. Let the heater cool, lower the temperature knob, turn the switch OFF and back ON once, and call service if F01 stays.
Safety first
Stop and check this first
- Scalding hazard: F01 means water inside the appliance exceeded 85 °C, so very hot water may remain in the pipes; always check water temperature carefully with your hand and avoid touching the hot inspection window.
- Only operate the water heater with its outer casing fully closed and never bypass the NTC probe or safety limiter; if you smell gas, close the gas shut-off valve, ventilate without using electrical switches, and call for assistance from outside.
Safe checks you can perform
- Check the cold water shut-off valve and let the unit cool
- Lower the hot water temperature on the rotary knob
- Single reset by turning the ON/OFF switch to OFF and back to ON
- Inspect the cold water inlet strainer, heat exchanger and electrical circuit
Leave these tasks to a qualified professional
- Do not attempt this professional task: Test the NTC temperature probe, safety limiter and PCB connections
- Do not attempt this professional task: Clean the heat exchanger and verify gas pressure and tightness
- Do not attempt this professional task: Clean the cold water inlet strainer and inspect the flow detector
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 the NTC temperature probe, safety limiter and PCB connections
What they doWith mains power unplugged, the technician checks the plug connections and wiring harness of the NTC probe (item 2) and safety temperature limiter (item 3) to the printed circuit board, replacing any defective part with an authorized original spare.
They must show youthe inspected NTC probe and safety limiter connectors and any component replaced.
In writingthe electrical circuit checks performed, the condition of the NTC probe and limiter, and any replacement part number.
Clean the heat exchanger and verify gas pressure and tightness
What they doThe technician cleans the heat exchanger using water, a soft brush, and neutral-pH soap if fouled, checks gas connection pressure at maximum heating load, and carries out a full functional and leak test.
They must show youthe water heater running in domestic hot water mode free of F01 and the completed tightness check.
In writingthe heat exchanger cleaning, the measured gas pressure, and the final test run result.
Clean the cold water inlet strainer and inspect the flow detector
What they doThe technician drains the hot water circuit, removes the inlet pipe and fittings, rinses the strainer under running water against the normal flow direction, checks the water flow demand sensor for dirt, and reassembles all joints with new gaskets.
They must show youthe cleaned cold water inlet strainer and the new gaskets used during reassembly.
In writingcode F01, the strainer cleaning and flow sensor inspection, the new gaskets fitted, and the date.
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 the cold water shut-off valve and let the unit cool
- Who:
- you.
- How:
- close all hot water taps, allow the water heater to cool down for several minutes, and check that the cold water shut-off valve on the inlet pipe is fully open.
- Result that matters:
- making sure incoming cold water flow is not throttled at the isolation valve and letting the water inside drop below 85 °C.
- If the cold water isolation valve was partly closed:
- open it fully before attempting a reset.
- If the cold water valve was already fully open:
- move on to checking the temperature adjustment knob.
- Evidence to keep:
- the position of the cold water shut-off valve and how many minutes you let the appliance cool.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08 · Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de funcionamiento 0020265481_04
Lower the hot water temperature on the rotary knob
- Who:
- you.
- How:
- check the domestic hot water temperature shown on the basic display and turn the upper rotary temperature knob to a moderate setting before drawing water again.
- Result that matters:
- preventing the burner from driving water temperature near the 85 °C cutout during low-flow draws.
- If it was set near maximum:
- turn it down to a moderate temperature and note the new value on the screen.
- If it was already set to a moderate temperature when F01 tripped:
- note this for the technician as a sign of flow restriction or sensor fault.
- Evidence to keep:
- the hot water temperature setting displayed when F01 occurred.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08 · Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de funcionamiento 0020265481_04
Single reset by turning the ON/OFF switch to OFF and back to ON
- Who:
- you.
- How:
- as instructed in Appendix A for code F.01, turn the rotary ON/OFF switch anticlockwise to OFF until the display goes out, then turn it clockwise back to ON once.
- Result that matters:
- checking whether the overheat lockout clears once the heater has cooled and water flow is restored.
- If F01 clears and hot water runs steadily:
- test the water temperature carefully with your hand first.
- If F01 remains on screen or comes back when a tap is opened:
- do not keep cycling the switch, contact Customer Service.
- Evidence to keep:
- whether turning the switch OFF and ON cleared F01 and whether it returned on the next hot water draw.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08 · Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de funcionamiento 0020265481_04
Inspect the cold water inlet strainer, heat exchanger and electrical circuit
- Who:
- authorized professional or Official Saunier Duval Technical Service.
- How:
- with the appliance unplugged and gas and water valves closed and drained, clean the cold water inlet strainer, inspect the water flow detector, and test the NTC probe and safety limiter wiring.
- Result that matters:
- pinpointing the water circuit or electrical circuit fault behind F01.
- If the cold water strainer or heat exchanger is fouled:
- clean it, reassemble with new gaskets throughout, and test hot water flow.
- If the water passage is clear but the NTC probe or wiring harness is faulty:
- repair the connection or fit an original spare part.
- Evidence to keep:
- condition of the inlet strainer, test readings on the NTC probe and limiter, and new gaskets fitted.
Internal servicing exposes 230 V electrical parts and gas joints: the unit must be unplugged and isolated by a qualified technician.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08
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
- Tankless gas water heater
Known code variants
- calentador Saunier Duval F01
- F 01
- F.01
- F01
- F1
- Opalia F.01
- Opalia F01
- Saunier Duval F.01
- Saunier Duval F01
- Saunier Duval water heater F01
What it means
In the installation and maintenance manual for the room-sealed Saunier Duval Opalia F 12/1 LR and F 14/1 LR water heaters (Appendix A, code F.01 Overheat, and Appendix B, code F01), this fault means the NTC probe has detected a water temperature above 85 °C and the gas supply has been interrupted. Appendix B lists a fault in the water circuit or in the electrical circuit as the underlying causes. Seeing F01 on the basic display does not by itself prove that the NTC sensor or any other part is broken.
Warnings and stop conditions
- Highsource verified
Scalding hazard: F01 means water inside the appliance exceeded 85 °C, so very hot water may remain in the pipes; always check water temperature carefully with your hand and avoid touching the hot inspection window.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08 · Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de funcionamiento 0020265481_04
- Highsource verified
Only operate the water heater with its outer casing fully closed and never bypass the NTC probe or safety limiter; if you smell gas, close the gas shut-off valve, ventilate without using electrical switches, and call for assistance from outside.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08 · Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de funcionamiento 0020265481_04
Symptoms and causes
Probable causes · in order
- Water temperature exceeding 85 °C at the NTC probeCommon
The NTC temperature sensor detects that water inside the heater has risen above 85 °C, immediately cutting off the gas supply to prevent scalding and thermal damage.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08
- Restricted flow or fault in the water circuitPossible
Appendix B attributes excessively high water temperature (F01) to a water circuit fault, such as a partially closed cold water shut-off valve or debris in the cold water inlet strainer.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08 · Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de funcionamiento 0020265481_04
- Dirty heat exchanger or incorrect maximum gas pressurePossible
Deposits on the heat exchanger fins or an out-of-range burner gas pressure at maximum heating load hinder heat transfer and push water temperature past the limit.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08
- Fault in the electrical circuit, NTC probe or safety limiterLess common
Appendix B also points to an electrical circuit fault (involving NTC probe item 2, safety temperature limiter item 3, or their wiring to the PCB) as a cause of F01.
Evidence: Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de instalación y mantenimiento 0020265480_08
Virtual technician
Does F01 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 · 2025 · manual
- 2
Saunier Duval Opalia F 12/1 LR y F 14/1 LR, instrucciones de funcionamiento 0020265481_04
Saunier Duval · 2020 · manual
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