- Boilers
- Gas boiler
03
Immergas 03 on a gas boiler: flue gas thermostat lockout
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Immergas 03 means the boiler has locked out because the flue gases overheated due to a fault. Check from outside that the flue terminal is not blocked, press Reset once and, if it returns, call the authorised technical service.
Safety first
Stop and check this first
- If you smell gas: Immergas says to close the meter or main gas tap and, if you can, the boiler's gas tap, open doors and windows, use no naked flames, do not smoke and do not touch switches, sockets, doorbells or phones. Leave the home and call your gas distributor's emergency number from the street.
- If you get a headache, dizziness or nausea while the boiler runs, there may be carbon monoxide: switch it off, ventilate, leave the home and call the emergency services. A CO alarm near the boiler warns you before symptoms start.
- Do not chain Resets with E03: after 5 in a row the boiler shows E08 and accepts no more Resets for an hour. If the lockout persists, Immergas says to call the Authorised Technical Assistance Centre.
Safe checks you can perform
- Flue terminal seen from outside
- Visible condensate pipe
- One Reset
- Fault list in the information menu
- Heat exchanger, condensate and ducts check by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Combustion analysis
- Do not attempt this professional task: Heat exchanger and condensate drain
- Do not attempt this professional task: Flue ducts
- Do not attempt this professional task: Flue sensor
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.
Combustion analysis
What they doUsing the chimney sweep function, the technician measures CO2 at the three reference outputs and CO. Immergas sets a maximum CO below 700 ppm at the annual check and below 500 ppm after a repair.
They must show youthe analyser printout.
In writingthe CO2 and CO values measured against the manufacturer's.
Heat exchanger and condensate drain
What they doThe technician cleans the flue side of the heat exchanger and the burner, removes deposits from the combustion chamber with nylon or sorghum brushes, as Immergas states, and checks that the trap and the whole condensate circuit are clear.
They must show youthe condition of the heat exchanger and the trap.
In writingwhat was cleaned and any insulating panel or seal replaced, with the reason.
Flue ducts
What they doThe technician runs the air intake and flue duct test, measures the pressure difference between the test points and compares it with the Immergas table and with the value from the first check.
They must show youthe pressure difference measured.
In writingthe measured value against the table and the resulting F0 setting.
Flue sensor
What they doThe technician reads the temperatures of the two flue sensors in the information menu (d 0.7 and d 1.4) and checks the sensor and its connection against the manufacturer's specification.
They must show youthe temperatures read and the sensor measurement.
In writingthe measured value against the manufacturer's and, if the sensor was replaced, why.
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.
Flue terminal seen from outside
- Who:
- you.
- How:
- from the street, the yard or the ground, without climbing ladders or onto the roof, look at the air intake and flue terminal. Immergas asks you to check it is not blocked.
- Result that matters:
- whether something is covering the outlet.
- If it is covered:
- do not dismantle or tamper with the ducts; tell the technician.
- If it is clear:
- rule out a visible blockage and go to the next check.
- Evidence to keep:
- a photo of the terminal.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
Visible condensate pipe
- Who:
- you.
- How:
- without opening the boiler, look at the condensate drain pipe along the part you can see down to the drain.
- Result that matters:
- whether the pipe is blocked or does not reach the drain.
- If you see dirt or a plug:
- tell the technician; a blocked condensate drain fits.
- If it is clean:
- rule out a visible blockage; the internal trap is checked by the technician.
- Evidence to keep:
- a photo of the pipe.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
One Reset
- Who:
- you.
- How:
- press the Reset button once, as Immergas states for E03.
- Result that matters:
- whether the boiler runs again and the code stays away.
- If it runs and does not return:
- note the date and time.
- If E03 returns:
- stop; Immergas says to call an authorised company, for example the Authorised Technical Assistance Centre. After 5 Resets in a row the boiler shows E08 and blocks Reset for an hour.
- Evidence to keep:
- a photo of the display with the code and a note of each Reset.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
Fault list in the information menu
- Who:
- you.
- How:
- press the information button for at least 1 second, step with the same button to d 0.8, which shows the last five faults, and note when E03 appears.
- Result that matters:
- whether E03 repeats and whether it appears with other codes.
- If E03 repeats:
- stop pressing Reset; tell the technician and show them the list.
- If it appears once and does not return:
- note the date and time and keep an eye on it.
- Evidence to keep:
- a photo of the fault list and a note of dates and times.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
Heat exchanger, condensate and ducts check by the technician
- Who:
- technician from an authorised company.
- How:
- checks the flue side of the heat exchanger, the trap and condensate circuit, the flue ducts, the flue sensor and the combustion.
- Result that matters:
- which fault overheats the flue gases.
- If there are deposits or a blocked condensate drain:
- they are cleaned before the boiler is used again.
- If the ducts or the combustion are out of specification:
- they are corrected.
- Evidence to keep:
- a job sheet with what was measured, cleaned and replaced.
Immergas reserves maintenance for an authorised company and forbids the user to dismantle or tamper with the air intake and flue ducts. Heat exchanger, trap, sensor and combustion are not user work.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
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
- Immergas
- Product type
- Gas boiler
Known code variants
- E03
- Error 03 Immergas
- Immergas E03
- Victrix 03
- Victrix E03
What it means
On the Victrix Zeus 25/32, E03 is the flue gas thermostat lockout: during normal operation a fault causes excessive flue gas overheating and the appliance locks out. The table provides for one Reset and, if the lockout persists, a call to an authorised company. It does not say which fault causes it: the flue side of the heat exchanger, the condensate drain, the flue ducts and the flue sensor are checked by the technician. The code does not prove the thermostat is faulty.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas: Immergas says to close the meter or main gas tap and, if you can, the boiler's gas tap, open doors and windows, use no naked flames, do not smoke and do not touch switches, sockets, doorbells or phones. Leave the home and call your gas distributor's emergency number from the street.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
- Criticaleditorial warning
If you get a headache, dizziness or nausea while the boiler runs, there may be carbon monoxide: switch it off, ventilate, leave the home and call the emergency services. A CO alarm near the boiler warns you before symptoms start.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
- Highsource verified
Do not chain Resets with E03: after 5 in a row the boiler shows E08 and accepts no more Resets for an hour. If the lockout persists, Immergas says to call the Authorised Technical Assistance Centre.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
Symptoms and causes
Probable causes · in order
- One-off overheatingPossible
Fits if one Reset clears it and E03 does not return. The Immergas table gives Reset as the remedy and a technician call only if the lockout persists.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
- Dirty heat exchanger on the flue sidePossible
Fits if the boiler has gone a while without its annual service. Immergas asks for the flue side of the heat exchanger to be cleaned every year and deposits removed from the combustion chamber.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
- Blocked condensate drainPossible
Fits if the visible condensate pipe is blocked or does not drain. Immergas states that a blocked trap can end up blocking the heat exchanger too.
Evidence: Immergas Victrix Zeus 25/32, instrucciones y advertencias para instalador, usuario y mantenimiento (1.042022SPA)
Virtual technician
Does 03 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
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