- Boilers
- Tankless gas water heater
A03
Cointra A03 on a gas water heater: overheat protection lockout
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On Cointra CPE T and Supreme E TS room-sealed water heaters, A03 is a lockout caused by the overheat protection. The manual points to the DHW sensor or to water not flowing. You may reset once; if A03 comes back, call the service engineer.
Safety first
Stop and check this first
- If you notice a gas smell when A03 shows, do not press RESET or any other key, avoid switches and plugs, and open doors and windows on your way out. Phone the gas emergency service once you are outside.
Safe checks you can perform
- Record A03 and the exact model
- Check whether other taps have water
- Try a single RESET
- Book a sensor and flow switch inspection
Leave these tasks to a qualified professional
- Do not attempt this professional task: Inspect the flow switch and water circulation
- Do not attempt this professional task: Check the DHW sensor position and condition
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.
Inspect the flow switch and water circulation
What they doIf the sensor is fine, the technician checks that the flow switch detects water passing and that the flow through the appliance is correct, as the table's remedy states.
They must show youthe flow switch response when a hot tap is opened.
In writingthe result of the check and any part replaced.
Check the DHW sensor position and condition
What they doThe authorised gas technician verifies that the dual safety and DHW sensor is firmly attached to the pipe and gives a consistent reading, as the fault table requires.
They must show youwhere the sensor is fitted and the reading obtained.
In writingthe sensor condition, whether it was refitted or replaced and the follow-up 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.
Record A03 and the exact model
- Who:
- you, reading the display and nothing else.
- How:
- photograph the display showing A03 and copy the model (CPE T or Supreme E TS) from the data plate or manual.
- Result that matters:
- confirming this is the overheat lockout and not another A code.
- If the display shows A41:
- that is the sensor position row, a different entry in the table.
- Evidence to keep:
- a photo of the code and the appliance model.
Evidence: Cointra CPE T, instrucción de uso, instalación y mantenimiento (cod. A73022110 Rev.03) · Cointra SUPREME E TS, instrucciones de uso, instalación y mantenimiento (cod. 3541A273 Rev.01)
Check whether other taps have water
- Who:
- you, without touching the water heater.
- How:
- open a cold tap in another room and see whether the flow is normal or whether the whole supply is cut off.
- Result that matters:
- knowing whether the lack of flow could come from the household supply.
- If no cold water comes out either:
- wait for the supply to return before using the heater.
- If the flow is normal:
- tell the technician, who will check the flow switch.
- Evidence to keep:
- the time of the outage or confirmation of normal flow.
Evidence: Cointra CPE T, instrucción de uso, instalación y mantenimiento (cod. A73022110 Rev.03) · Cointra SUPREME E TS, instrucciones de uso, instalación y mantenimiento (cod. 3541A273 Rev.01)
Try a single RESET
- Who:
- you, with no gas smell or CO alarm.
- How:
- press the RESET key for one second, as the manual describes for A lockouts, then open a hot tap.
- Result that matters:
- whether A03 clears and the water heats normally.
- If it comes back:
- do not keep resetting; the protection is responding to a real cause.
- If it clears:
- note the date and watch for a repeat.
- Evidence to keep:
- the reset outcome and the date.
Evidence: Cointra CPE T, instrucción de uso, instalación y mantenimiento (cod. A73022110 Rev.03) · Cointra SUPREME E TS, instrucciones de uso, instalación y mantenimiento (cod. 3541A273 Rev.01)
Book a sensor and flow switch inspection
- Who:
- the gas technician answering your A03 call.
- How:
- they should compare A03 with Cointra's table before proposing parts.
- Result that matters:
- whether the protection tripped because of the sensor or because of low flow.
- If the sensor has shifted:
- refitting and testing it may be enough.
- If the flow switch does not respond:
- its repair must be justified.
- Evidence to keep:
- a job sheet stating the confirmed A03 cause.
The sensor and flow switch sit inside the casing; do not remove it yourself.
Evidence: Cointra CPE T, instrucción de uso, instalación y mantenimiento (cod. A73022110 Rev.03) · Cointra SUPREME E TS, instrucciones de uso, instalación y mantenimiento (cod. 3541A273 Rev.01)
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
- Cointra
- Product type
- Tankless gas water heater
Known code variants
- A-03
- Anomalía A03 Ferroli
- Beretta A 03
- calentador Cointra A03
- Ciao Green A03
- Cointra A03
- Cointra water heater A03
- CPE T A03
- Error A03 Beretta
- Error A03 Ferroli
- Ferroli A03
- Ferroli A03 boiler
- Ferroli A03 caldera
- Ferroli error A03
- Supreme E TS A03
What it means
A03 appears when the water heater stops the burner because its protection against excessive water temperature has tripped. Cointra links this lockout to two situations: a faulty or badly positioned DHW sensor, or a lack of water flow that calls for a flow switch check. On the CPE T the sensor is a dual unit combining the safety and DHW reading functions. Because it starts with A, the lockout is permanent and will not clear by itself: it needs the RESET key or a technician.
Warnings and stop conditions
- Criticaleditorial warning
If you notice a gas smell when A03 shows, do not press RESET or any other key, avoid switches and plugs, and open doors and windows on your way out. Phone the gas emergency service once you are outside.
Evidence: Cointra CPE T, instrucción de uso, instalación y mantenimiento (cod. A73022110 Rev.03) · Cointra SUPREME E TS, instrucciones de uso, instalación y mantenimiento (cod. 3541A273 Rev.01)
Symptoms and causes
Probable causes · in order
- Faulty or displaced DHW sensorPossible
The manufacturer's table asks for the position and operation of the DHW sensor to be checked. On the CPE T this sensor is a dual safety and DHW unit, so a false reading or poor contact with the pipe can trip the protection.
Evidence: Cointra CPE T, instrucción de uso, instalación y mantenimiento (cod. A73022110 Rev.03) · Cointra SUPREME E TS, instrucciones de uso, instalación y mantenimiento (cod. 3541A273 Rev.01)
- Water not flowing through the heaterPossible
Cointra lists no water circulation as the second cause and refers to a flow switch check. The flow switch is the component that monitors water passing through the appliance, and it is on the manufacturer's annual service list.
Evidence: Cointra CPE T, instrucción de uso, instalación y mantenimiento (cod. A73022110 Rev.03) · Cointra SUPREME E TS, instrucciones de uso, instalación y mantenimiento (cod. 3541A273 Rev.01)
Virtual technician
Does A03 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
Cointra CPE T, instrucción de uso, instalación y mantenimiento (cod. A73022110 Rev.03)
Cointra · 2018 · manual
- 2
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