- Boilers
- Electric water heater
042
Ariston 042 on a Nuos Plus heat pump water heater: evaporator blocked
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Low
Quick answer
On an Ariston Nuos Plus, 042 means the evaporator is blocked: the heat pump stops and the electric element keeps heating. Switch the heater off and check that nothing covers the air inlets and outlets or their ducts; if it returns, call the technician.
Safety first
Stop and check this first
- Do not clean the evaporator yourself or use products not recommended by Ariston: the manufacturer forbids it because of the fire or explosion risk with R290.
- Ariston reserves maintenance and repairs for authorised personnel with suitable equipment. Do not open the covers: inside there is mains voltage and the refrigerant circuit.
Safe checks you can perform
- Which heating group still works
- Air openings and ducts
- Evaporator inspection
Leave these tasks to a qualified professional
- Do not attempt this professional task: Evaporator and ducting inspection
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.
Evaporator and ducting inspection
What they doThe technician inspects the evaporator and checks duct lengths, grilles and distances against Ariston's manual.
They must show youphotos of the evaporator and the ducting.
In writingwhat blockage was found, what was cleaned or corrected and with what.
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.
Which heating group still works
- Who:
- you.
- How:
- look at the display: Ariston says that if the error is in the heat pump, the HP symbol flashes; if it is in the electric element, the element symbol flashes; if both are affected, both flash. Take a photo showing code 042.
- Result that matters:
- Ariston explains that the heater keeps supplying hot water if the error affects only one of the two heating groups.
- If only HP flashes:
- the electric element keeps heating; you will have hot water until the technician arrives.
- If the element symbol or both flash:
- you may have no hot water; book the visit as soon as possible.
- Evidence to keep:
- a photo of the display with the code and the flashing symbols.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
Air openings and ducts
- Who:
- you.
- How:
- switch the heater off, as Ariston asks, and look without opening anything at the intake and exhaust openings on top and, if fitted, the ducts and outside grilles.
- Result that matters:
- Ariston asks for a check for obstructions and forbids outside grilles with high pressure loss, such as insect screens.
- If something blocks the air or a duct is crushed or loose:
- remove it or have the installer correct it, then switch back on.
- If everything is clear and 042 returns:
- the blockage may be inside; move on to the technician.
- Evidence to keep:
- photos of the openings, ducts and grilles.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
Evaporator inspection
- Who:
- an authorised Ariston service technician.
- How:
- with the appliance disconnected, opens the casing and checks the evaporator and the internal airflow; checks the ducting against the configurations in the manual.
- Result that matters:
- where the blockage is.
- If the evaporator is dirty or blocked:
- cleaning with means approved by Ariston confirms the cause if 042 does not return.
- If it is clean:
- the cause is in the ducting or another component the technician must measure.
- Evidence to keep:
- before and after photos of the evaporator and a job sheet.
Inside there is mains voltage and R290 refrigerant. Ariston forbids cleaning with means not recommended by the manufacturer.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
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
- Ariston
- Product type
- Electric water heater
Known code variants
- 42
- Ariston error 042
- Ariston Nuos error 042
- Error 042 Ariston
- Nuos 042
What it means
Ariston links 042 to a blocked evaporator on the Nuos Plus S2 Wi-Fi: the heat pump goes OFF and the electric element stays ON. The action it gives is to switch the appliance off and check for obstructions in the evaporator and the casing. The evaporator takes heat from the air entering at the top; if the air cannot pass, because of objects in front, crushed ducts or high-loss grilles, the heat exchange drops. The code does not say where the blockage is.
Warnings and stop conditions
- Highsource verified
Do not clean the evaporator yourself or use products not recommended by Ariston: the manufacturer forbids it because of the fire or explosion risk with R290.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
- Highsource verified
Ariston reserves maintenance and repairs for authorised personnel with suitable equipment. Do not open the covers: inside there is mains voltage and the refrigerant circuit.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
Symptoms and causes
Probable causes · in order
- Air inlet or outlet coveredCommon
Objects, dust or clothes in front of the top openings stop the airflow. It can be seen without opening the heater.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
- Ducts or grilles restricting the airPossible
Ariston forbids outside grilles with high pressure loss, such as insect screens, and requires at least 37 cm between inlet and outlet. It is told apart by checking the ducted installation.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
- Dirt on the evaporatorPossible
If openings and ducts are clear, the blockage may be in the evaporator itself, which only the technician checks with the unit open.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
Virtual technician
Does 042 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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