- Boilers
- Electric water heater
021
Ariston 021 on a Nuos Plus heat pump water heater: possible refrigerant leak
Risk level
High
Professional inspection is recommended.
Urgency
Medium
Quick answer
On an Ariston Nuos Plus heat pump water heater, 021 means a possible refrigerant gas leak. The heat pump stops and the electric element keeps heating. Ventilate, keep flames and sparks away and call a licensed refrigeration technician.
Safety first
Stop and check this first
- The Nuos Plus holds 0.15 kg of R290 (propane) refrigerant, which is flammable and odourless. Ariston forbids repairing the refrigerant circuit at the installation site and reserves recharging for licensed refrigeration technicians. Keep flames and sparking devices away from the heater.
- Ariston warns that water above 50 °C at the taps can cause serious burns instantly; with the electric element the Nuos accepts set points up to 75 °C. Check the temperature before showering.
Safe checks you can perform
- Which heating group still works
- Smell, ventilation and ignition sources
- Sensor check and leak search
Leave these tasks to a qualified professional
- Do not attempt this professional task: Checking the sensor before the circuit
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.
Checking the sensor before the circuit
What they doThe technician measures the compressor inlet sensor and, if it is correct, searches for the leak with a detector suitable for R290.
They must show youthe sensor reading and where the leak is.
In writingthe detection result, the amount of R290 recovered and recharged and the workshop where the circuit was repaired.
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 021.
- 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
Smell, ventilation and ignition sources
- Who:
- you.
- How:
- ventilate the room where the heater is, switch off any flame or sparking device nearby and do not smoke. Do not open the covers.
- Result that matters:
- Ariston reminds you that R290 is flammable and odourless, so not smelling anything does not rule out a leak.
- If the room is small or closed:
- keep it ventilated until the visit.
- If the heater is in a well ventilated place:
- keep using hot water from the electric element until the technician arrives.
- Evidence to keep:
- a photo of where the heater is and of the code.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
Sensor check and leak search
- Who:
- a refrigeration technician licensed for flammable refrigerants such as R290.
- How:
- verifies the compressor inlet sensor; if it is correct, searches for the leak with a detector calibrated for R290 and with no ignition sources, as Ariston requires.
- Result that matters:
- whether the sensor reading is correct and whether a leak is located.
- If the sensor reads wrongly:
- the alert came from the sensor and is fixed without opening the circuit.
- If a leak is located:
- the repair follows Ariston, which forbids repairing the circuit at the installation site.
- Evidence to keep:
- a report with the sensor reading and the leak detection result.
Flammable refrigerant circuit: licensed refrigeration technicians with suitable equipment only.
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
- 21
- Ariston error 021
- Ariston Nuos error 021
- Error 021 Ariston
- Nuos 021
What it means
In the Nuos Plus S2 Wi-Fi error table, Ariston links 021 to a gas leak: the heat pump goes OFF and the electric element stays ON. The first thing it asks the technician to do is verify the compressor inlet sensor; only if the error persists, recover the residual gas, find and repair the leak, pull a vacuum and recharge the correct amount. The refrigerant is R290 (propane). The code does not prove a leak: a sensor that reads wrongly gives the same alert.
Warnings and stop conditions
- Criticalsource verified
The Nuos Plus holds 0.15 kg of R290 (propane) refrigerant, which is flammable and odourless. Ariston forbids repairing the refrigerant circuit at the installation site and reserves recharging for licensed refrigeration technicians. Keep flames and sparking devices away from 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
- Highsource verified
Ariston warns that water above 50 °C at the taps can cause serious burns instantly; with the electric element the Nuos accepts set points up to 75 °C. Check the temperature before showering.
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
- Leak in the refrigerant circuitCommon
This is what Ariston points to for 021. It is confirmed with leak detection suitable for R290, not by the code.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
- Compressor inlet sensorPossible
Ariston has it checked first. If it reads wrongly, the gas leak alert can be false and the circuit need not be opened.
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 021 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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