- Boilers
- Electric water heater
W24
Thermor W24 on an Aeromax water heater: air temperature outside the heat pump range
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Low
Quick answer
On Thermor heat pump water heaters, W24, Info 24 or error 24 mean the air entering the heat pump is too cold or too hot and the heat pump stops. Check the mode so the electric back-up gives you hot water.
Safety first
Stop and check this first
- Do not open the heater's cover: inside there is mains voltage and, on heat pump models, the refrigerant circuit. That diagnosis is for an installer or a refrigeration technician.
- When the electric back-up or emergency mode gives hot water again, test the temperature before showering, especially for children or older people.
Safe checks you can perform
- Operating mode and hot water
- Room or outdoor temperature
- Air sensor reading
Leave these tasks to a qualified professional
- Do not attempt this professional task: Comparing the sensor with the real temperature
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.
Comparing the sensor with the real temperature
What they doThe technician compares the temperature the air sensor shows with the real one before proposing a replacement.
They must show youthe sensor reading next to the thermometer reading.
In writingboth temperatures and, if the sensor is 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.
Operating mode and hot water
- Who:
- you.
- How:
- check on the digital control which mode is active (AUTO, Manual ECO on or off, ECO) and whether hot water comes out of a tap. Take a photo showing W24.
- Result that matters:
- Thermor explains that in AUTO with Manual ECO off the electric back-up, fitted at mid height of the tank, comes on, while in Manual ECO on or ECO it does not (except on the Airlis) and there is no hot water.
- If you are in Manual ECO on or ECO:
- switch to AUTO, Manual ECO off or the emergency mode described in your model's manual to get hot water until the technician arrives.
- If you are in AUTO and there is less hot water:
- that is expected, because only the water above the element is heated.
- Evidence to keep:
- a photo of the code and the active mode, with the date.
Evidence: Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
Room or outdoor temperature
- Who:
- you.
- How:
- measure with a thermometer the temperature of the room where the heater is or, if it draws outside air or is a Split, the outdoor temperature, and note the time.
- Result that matters:
- Thermor says an ambient air model without ducts needs a room above 7 °C and one ducted outside with two ducts triggers below -5 °C; in summer, heat also causes it.
- If the temperature is outside those limits:
- the message is consistent; it will clear when the temperature returns to range.
- If the temperature is normal and the message stays:
- the sensor may be reading wrongly; go on to the sensor check.
- Evidence to keep:
- a photo of the thermometer with the time and of the code.
Evidence: Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
Air sensor reading
- Who:
- an installer or qualified technician.
- How:
- on the digital control, reads the instantaneous temperature of the air sensor and compares it with a thermometer reading next to the air inlet.
- Result that matters:
- whether the sensor reading matches the real temperature.
- If they match:
- the message is genuine and there is nothing to repair.
- If they do not match:
- Thermor says to replace the sensor.
- Evidence to keep:
- a photo of the on-screen reading and the thermometer.
Replacing the sensor means opening the cover or the outdoor unit, with mains voltage. Technician only.
Evidence: Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
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
- Thermor
- Product type
- Electric water heater
Known code variants
- Err 24
- Erreur 24
- INF24
- Info 24
- Thermor W24
- W.24
What it means
Thermor explains that error 24 is really an information message, Info 24 or INF24: it appears when the sensor measuring air entering the heat pump detects a temperature too low or too high for the refrigerant's operating range. The heat pump stops so the compressor is not overworked. It can come from the room or outdoor climate or from a faulty sensor. The code alone does not distinguish air really out of range from a sensor that reads wrongly.
Warnings and stop conditions
- Higheditorial warning
Do not open the heater's cover: inside there is mains voltage and, on heat pump models, the refrigerant circuit. That diagnosis is for an installer or a refrigeration technician.
Evidence: Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
- Mediumeditorial warning
When the electric back-up or emergency mode gives hot water again, test the temperature before showering, especially for children or older people.
Evidence: Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
Symptoms and causes
Probable causes · in order
- Air outside the refrigerant's rangeCommon
On an ambient air model without ducts, the room must be above 7 °C; if it draws outside air through two ducts, it triggers below -5 °C. Summer heat also triggers it.
Evidence: Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
- Outdoor climate on Split modelsPossible
On Split models the sensor is in the outdoor unit, so strong heat or intense cold can trigger the message.
Evidence: Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
- Faulty air sensorPossible
Thermor says to compare the temperature the sensor shows on the digital control with the real one and replace it if they do not match.
Evidence: Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
Virtual technician
Does W24 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
Comment résoudre un problème de chauffe-eau qui affiche une erreur 24 ou une Info24 ?
Thermor · 2026 · official_doc
- 2
Mon chauffe-eau affiche une erreur, que faire ?
Thermor · 2025 · official_doc
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