- Boilers
- Electric water heater
218
Ariston 218 on a Nuos Plus heat pump water heater: dome hot water sensor
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Medium
Quick answer
On an Ariston Nuos Plus, 218 means the dome NTC sensor, the hot water sensor, is open or short circuited. The heat pump stops and the electric element keeps heating. Photograph the code and ask the technician to measure the sensor.
Safety first
Stop and check this first
- 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.
- 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
- Restart and whether the code returns
- Dome sensor measurement
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measuring the dome NTC 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.
Measuring the dome NTC sensor
What they doThe technician measures the sensor and checks its connection and seating, as Ariston asks before any work.
They must show youthe measured value against Ariston's specification.
In writingwhat was found and which part was replaced.
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 218.
- 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
Restart and whether the code returns
- Who:
- you.
- How:
- switch the heater off with the ON/OFF button, wait a moment and switch it back on; watch whether 218 reappears.
- Result that matters:
- whether the error persists or was a one-off.
- If 218 does not return:
- note the date; if it repeats, tell the technician.
- If 218 returns:
- the sensor or its connection is still out of range; book the visit.
- Evidence to keep:
- a photo of the code and a note of how often it appeared.
Evidence: Ariston Nuos Plus S2 Wi-Fi, calentador de agua con bomba de calor: instrucciones para la instalación, el uso y el mantenimiento
Dome sensor measurement
- Who:
- an authorised Ariston service technician.
- How:
- with the appliance disconnected, checks the sensor connection to the main board and its seating in the housing, and measures the NTC with a multimeter.
- Result that matters:
- whether the sensor measures within Ariston's specification.
- If it reads open or short circuited:
- the sensor is confirmed.
- If it reads correctly:
- the cause is the cable or the connector.
- Evidence to keep:
- a job sheet with the measured value.
Opening the unit exposes mains voltage and the R290 circuit. Technician 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
- Ariston error 218
- Ariston Nuos error 218
- Error 218 Ariston
- Nuos 218
What it means
Ariston links 218 to the dome NTC sensor, which measures hot water at the top of the tank, when the control reads it as an open or short circuit. With this error the heat pump goes OFF and the electric element stays ON. The action it gives is to check that the sensor works correctly, and before any work it asks for the electrical connection of components to the main board and the positioning of the probes in their housings to be checked. The code does not distinguish sensor, cable or connector.
Warnings and stop conditions
- 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
- 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
- Dome NTC sensor open or short circuitedCommon
This is the condition Ariston describes. It is confirmed by measuring the sensor, 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
- Sensor connection or positioningPossible
Ariston asks for the electrical connection to the main board and the seating of each NTC probe in its housing to be checked before anything is replaced.
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 218 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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