Ariston
The Ariston Nuos_Plus_Installation_Servicing_Use is an integrated air-source heat pump water heater with a nominal capacity of 2.775 kW, using R134a refrigerant, and a 5-year tank warranty.
The Ariston Nuos_Plus_Installation_Servicing_Use is an air-source heat pump water heater designed for domestic hot water production in UK properties. This integrated unit offers an efficient solution for homeowners and provides essential technical data for heating engineers. Key specifications include a nominal capacity of 2.775 kW, utilising R134a refrigerant, and a maximum flow temperature of 65°C. This page details operational parameters, installation requirements, fault codes, and a comprehensive service guide.
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Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
5 Years (Tank) and 2 Years (electrical components). Guarantee is subject to correct installation, commissioning, and annual servicing as detailed in the manual. Annual service required after 12 months to continue guarantee.
The Ariston Nuos Plus range represents an integrated air-source heat pump water heater solution for domestic hot water requirements within the UK. Designed for efficiency, these units extract heat from the ambient air to warm stored water. The appliance operates with a nominal capacity of 2.775 kW at an ambient temperature of 7°C, capable of delivering a maximum flow temperature of 65°C, ensuring ample hot water for typical household demands.
Refrigeration is managed by R134a, with a charge of 1.28 kg. This refrigerant choice, while effective, has a higher Global Warming Potential (GWP) compared to newer alternatives like R290 or R32, a consideration for long-term environmental strategies. The system incorporates an automatic hot gas defrost method, ensuring continuous operation even in colder conditions down to -5°C.
Installation requires specific clearances to ensure optimal airflow and service access. A minimum of 400mm clearance is specified for both sides and the front of the unit, with 100mm behind and 50mm above. Furthermore, a minimum air volume of 20m³ is required in the installation space. Electrical connection is straightforward, requiring a 230V, 50Hz, single-phase supply, protected by a 13A MCB. Hydraulic connections are designed for 22mm pipework, supporting a maximum operating pressure of 6 bar.
The Nuos Plus offers various tank capacities, with models such as the Nuos 200d providing 200 litres and the Nuos 250i offering 250 litres. Reheat times vary by model, with the 200d taking approximately 347 minutes and the 250i requiring 389 minutes (HP+HE mode). Sound emissions are rated at 56 dB sound pressure, measured at 2m, which is a factor for siting considerations in residential areas.
Maintenance is critical for sustained performance and warranty validity. Ariston specifies an annual service interval of 12 months. The warranty structure includes a 5-year guarantee on the tank and 2 years on electrical components, conditional on correct installation, commissioning, and annual servicing. Engineers should refer to the detailed service steps, which include checking the electric heater element, inspecting the internal cylinder, cleaning the evaporator and fan, and verifying the operation of safety valves and the expansion vessel. Fault codes, such as E1 for lack of water or H3 for compressor fault/gas leak, provide diagnostic guidance for engineers during servicing or troubleshooting.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/heat-pumps/ariston/nuos-200d#fault-e1 to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| E1 | Heating occurs without any water in the water tank Show causes & actionsLikely causes
User action Turn off the appliance. Verify the causes of the lack of water (leakage, faulty hydraulic connections, etc.). Engineer action Turn off the appliance. Verify the causes of the lack of water (leakage, faulty hydraulic connections, etc.). | Details |
| E2 | Excessive temperature of the water in the tank Show causes & actionsUser action Turn the appliance off then wait until the water temperature decreases; if the problem persists, contact technical advice* Engineer action Turn the appliance off then wait until the water temperature decreases; if the problem persists, contact technical advice* | Details |
| E4 | Sensor fault - heating element zone Show causes & actionsEngineer action Check or replace the heating element zone sensors, if necessary. | Details |
| E5 | Excessive difference between the temperatures of the heating element zone sensors Show causes & actionsEngineer action Check or replace the sensors, if necessary | Details |
| H1 | Excessive pressure on the refrigeration circuit, or faulty reading of the pressure switch Show causes & actionsUser action Try to restart the device; if error persists contact technical advice* Engineer action Try to restart the device; if error persists contact technical advice* | Details |
| H2 | Circuit in low pressure or fan fault Show causes & actionsLikely causes
User action Turn off the appliance. Check that the fan is not broken and that the evaporator is not obstructed. Check whether the 4 way valve functions properly and replace it if necessary. Check the grids and ducts are not blocked and are clear. Engineer action Turn off the appliance. Check that the fan is not broken and that the evaporator is not obstructed. Check whether the 4 way valve functions properly and replace it if necessary. Check the grids and ducts are not blocked and are clear. | Details |
| H3 | Compressor fault or gas leak Show causes & actionsLikely causes
User action Turn off the appliance. Check that the evaporator is not obstructed. Verify whether the wirings and the compressor functions properly and/or check for any refrigerant gas leakages. Check or replace the evaporator sensor. Check the grids and ducts are not blocked and are clear. Engineer action Turn off the appliance. Check that the evaporator is not obstructed. Verify whether the wirings and the compressor functions properly and/or check for any refrigerant gas leakages. Check or replace the evaporator sensor. Check the grids and ducts are not blocked and are clear. | Details |
| H4 | Evaporator obstructed Show causes & actionsLikely causes
User action Turn off the appliance. Check that the evaporator is not obstructed. Check the grids and ducts are not blocked and are clear. Engineer action Turn off the appliance. Check that the evaporator is not obstructed. Check the grids and ducts are not blocked and are clear. | Details |
| H5 | Fan fault Show causes & actionsLikely causes
User action Turn off the appliance. Verify that there are no physical impediments to the movement of fan blades, check the wiring of connection with circuit boards. Engineer action Turn off the appliance. Verify that there are no physical impediments to the movement of fan blades, check the wiring of connection with circuit boards. | Details |
| H6 | Air sensor fault Show causes & actionsUser action Check the proper connection of the probe cable between the two units. Verify whether the sensor is properly connected and positioned and replace it if necessary. Engineer action Check the proper connection of the probe cable between the two units. Verify whether the sensor is properly connected and positioned and replace it if necessary. | Details |
| H7 | Evaporator sensor fault Show causes & actionsUser action Check the proper connection of the probe cable between the two units. Verify whether the sensor is properly connected and positioned and replace it if necessary. Engineer action Check the proper connection of the probe cable between the two units. Verify whether the sensor is properly connected and positioned and replace it if necessary. | Details |
| H8 | Hot water sensor fault Show causes & actionsUser action Check whether the sensor is properly connected and positioned and replace it if necessary. Engineer action Check whether the sensor is properly connected and positioned and replace it if necessary. | Details |
| H9 | Active defrost fault Show causes & actionsLikely causes
User action Check that the fan is not broken and that the evaporator is not obstructed. Check whether the 4 way valve functions properly and replace it if necessary. Check the grids and ducts are not blocked and are clear. Engineer action Check that the fan is not broken and that the evaporator is not obstructed. Check whether the 4 way valve functions properly and replace it if necessary. Check the grids and ducts are not blocked and are clear. | Details |
| F1 | PCB fault Show causes & actionsUser action Try turning the appliance off then on again and verify the operation of the control boards, if necessary replace it. Engineer action Try turning the appliance off then on again and verify the operation of the control boards, if necessary replace it. | Details |
| F2 | Excessive number of ON/OFF (RELEASE) Show causes & actionsUser action Temporarily disconnect the product mains. Engineer action Temporarily disconnect the product mains. | Details |
| 3 | Lack of communication between the PCB and interface Show causes & actionsUser action Try turning the appliance off then on again and verify the operation of the control boards and replace them, if necessary. Engineer action Try turning the appliance off then on again and verify the operation of the control boards and replace them, if necessary. | Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
User: Turn off the appliance. Verify the causes of the lack of water (leakage, faulty hydraulic connections, etc.).
Engineer: Turn off the appliance. Verify the causes of the lack of water (leakage, faulty hydraulic connections, etc.).
Triggered by fault code E1.
User: Turn the appliance off then wait until the water temperature decreases; if the problem persists, contact technical advice*
Engineer: Turn the appliance off then wait until the water temperature decreases; if the problem persists, contact technical advice*
Triggered by fault code E2.
Engineer: Check or replace the heating element zone sensors, if necessary.
Triggered by fault code E4.
Common questions from engineers and homeowners about the Ariston Nuos 200d.
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Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 30 April 2026.
Engineer: Check or replace the sensors, if necessary
Triggered by fault code E5.
User: Try to restart the device; if error persists contact technical advice*
Engineer: Try to restart the device; if error persists contact technical advice*
Triggered by fault code H1.