- Heat pumps
- Air-to-water heat pump
923
Ariston 923 on a Nimbus heat pump: heating circuit pressure error
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On Ariston Nimbus heat pumps, error 923 points to a pressure problem in the heating circuit. Once the circuit has cooled, check the gauge: Ariston wants 0.5 to 1.5 bar. If it is low and your installer showed you the filling cock, top up to 1.2 bar and close it.
Safety first
Stop and check this first
- Never exceed 3 bar when topping up and close the filling cock afterwards; a dripping cock can push the pressure up without you noticing.
- Ariston forbids disconnecting the power supply if the outdoor temperature can fall below zero, because of frost risk; do not switch the heat pump off in winter just to clear the message.
Safe checks you can perform
- Read the system gauge with the system cold
- Top up only with the filling cock you were shown
- Look for visible signs of a leak
- Record the full SENSYS HD message
Leave these tasks to a qualified professional
- Do not attempt this professional task: Trace the water leak
- Do not attempt this professional task: Test the pressure switch and its wiring
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.
Trace the water leak
What they doThe installer works along the hydraulic circuit, checks joints, valves, air vents and the expansion vessel, and tests whether pressure falls with the system idle.
They must show youwhere the leak was, or the pressure test that rules one out.
In writingthe cause found, the repair made and the final cold pressure.
Test the pressure switch and its wiring
What they doWith the unit isolated, the technician inspects the pressure switch plug and cabling and compares its signal with the real reading on the gauge.
They must show youthe gauge reading next to what the unit reports.
In writingthe condition of the pressure switch, whether it was replaced and the part number.
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.
Read the system gauge with the system cold
- Who:
- you, no tools needed.
- How:
- let the system cool down and read the heating circuit pressure gauge. Ariston gives a correct cold range of 0.5 bar to 1.5 bar, and a maximum system pressure of 3 bar.
- Result that matters:
- knowing whether the real pressure sits inside or outside Ariston's range.
- If the needle is below 0.5 bar:
- the code matches a lack of water; top up as below or call your installer.
- If pressure is between 0.5 and 1.5 bar and 923 stays:
- suspicion moves to the pressure switch or its wiring, which is technician work.
- Evidence to keep:
- photo of the gauge reading and of the screen showing 923.
Evidence: Ariston NIMBUS S NET, manual de uso para el usuario (ES/PT) · Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
Top up only with the filling cock you were shown
- Who:
- you, and only if your installer showed you the filling cock on your system.
- How:
- open the filling cock slowly while watching the gauge. Ariston says to close it once the average value of 1.2 bar is reached. Do not go higher and leave other valves and the air vents alone.
- Result that matters:
- about 1.2 bar on the gauge with the filling cock fully closed.
- If pressure holds over the next days and 923 clears:
- note the date you topped up.
- If it drops again quickly or you need to fill once a month or more:
- stop topping up and call the installer, as Ariston links this to an installation problem.
- Evidence to keep:
- date plus pressure before and after each top up.
Evidence: Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
Look for visible signs of a leak
- Who:
- you, looking only, without dismantling anything.
- How:
- check radiators, the underfloor manifold, visible valves and the exposed pipes around the indoor unit. Look for drips, damp patches, dried white scale or puddles under the equipment. Do not open covers or panels.
- Result that matters:
- finding or ruling out a leak you can see.
- If you find drips or water marks:
- take photos and call the installer before refilling.
- If there is no trace of water:
- the leak may be hidden or the switch may be at fault; tell the technician.
- Evidence to keep:
- photos of any wet spot with its location.
Evidence: Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
Record the full SENSYS HD message
- Who:
- you.
- How:
- when the pop up window appears, write down the code, the description and the device that raised it, as the user manual describes. If it closes, the Back key reopens it. Also check whether 2P8 is listed.
- Result that matters:
- an exact record of the message for the technician.
- If 923 and 2P8 appear together:
- low pressure is the main lead.
- If only 923 shows while the gauge reads normal:
- say so, because it points towards the pressure switch.
- Evidence to keep:
- photo of the error window with code, description and device.
Evidence: Ariston NIMBUS S NET, manual de uso para el usuario (ES/PT) · Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
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
- Heat pumps
- Brand
- Ariston
- Product type
- Air-to-water heat pump
Known code variants
- aerotermia Ariston 923
- Ariston 923
- Ariston heat pump 923
- Ariston heating circuit pressure error
- Ariston Nimbus error 923
- E923
- Error 923
- error presión circuito calefacción Ariston
- Nimbus 923
- Nimbus Compact 923
- Nimbus Plus 923
- Nimbus Pocket 923
- Sensys HD 923
What it means
The indoor unit error list in the Ariston Nimbus Plus S NET R32 installation manual (UK, 2023) gives 923 as Heating circuit pressure error. Ariston's resolution covers three things: water leaks in the hydraulic circuit, a faulty pressure switch, or defective pressure switch cabling. The Spanish NIMBUS manuals carry the same row, and the code shows on the SENSYS HD interface. A 923 on its own does not prove the pressure switch has failed; the actual water pressure has to be read first. The Spanish list also has 2P8, a low pressure warning with the same resolution.
Warnings and stop conditions
- Loweditorial warning
Never exceed 3 bar when topping up and close the filling cock afterwards; a dripping cock can push the pressure up without you noticing.
Evidence: Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
- Mediumsource verified
Ariston forbids disconnecting the power supply if the outdoor temperature can fall below zero, because of frost risk; do not switch the heat pump off in winter just to clear the message.
Evidence: Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
Symptoms and causes
Probable causes · in order
- Low water pressure from a leakCommon
Ariston's first instruction is to look for water leaks in the hydraulic circuit; even a slow drip lowers the pressure until the error trips.
Evidence: Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
- Air leaving the system after fillingPossible
The manual notes that not all air comes out during filling and that the automatic air vents remove it in the first hours, so the pressure can sag and need topping up.
Evidence: Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
- Faulty pressure switchPossible
The error table lists a faulty pressure switch, which can report a false low reading even when the circuit pressure is fine.
Evidence: Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
- Pressure switch cabling faultLess common
Ariston asks for the pressure switch connection to be checked and the part replaced if necessary; a loose plug or damaged wire also raises 923.
Evidence: Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
Virtual technician
Does 923 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
Ariston NIMBUS POCKET M NET R32, instrucciones técnicas de instalación y mantenimiento
Ariston · 2022 · manual
- 2
Ariston NIMBUS S NET, manual de uso para el usuario (ES/PT)
Ariston · 2022 · manual
- 3
Ariston Nimbus Plus S NET R32 technical instructions for installation and maintenance (UK)
Ariston · 2023 · manual
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