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  - the ultimate in simplicity for under-sink heaters

The Mini is a 5 litre point of use water heater, with an impressive 6 minute recovery time. The small size makes the Mini ideal for under sink fitting in office buildings etc. where the central hot water supply is located at a distance. The Mini can be installed both vertically and horizontally, and has a factory fitted thermostat adjustable 30°C – 60.

The OSO MINI RM5 is perfect for point of use “under sink” water heater. The 3kW element will heat the 5 litre capacity from cold in less than 6 minutes. The unit will be most efficient when fitted horizontally. Wall mounting brackets are provided with the cylinder.

Although The RM5 is an unvented cylinder, it requires no expansion vessel, although an expansion relief valve for connection to a waste pipe is supplied. Domestic water expansion is accommodated safely and legally within the cylinder and associated pipework.


No check valve should be fitted within 2m of the RM5, to avoid the need for an expansion vessel.

Temperature control is achieved through a factory fitted adjustable thermostat, with an additional overheat safety cut out. An electrical cable is supplied factory fitted to the cylinder for connection to the mains supply.

Key advantages:

  • Can be mounted both horizontally and vertically without the need for expansion vessel.
  • Only 6 minutes recovery time from cold water to 60°C.
  • Ideal for office buildings etc., where central heating is located at a distance.
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Technical Specifications
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Mini is suitable as a point of use water heater, ideal for under sink fitting in office buildings etc.



Prod. nr. Product description Capacity Hot water - 40°C Heat-up (best) - 15°C - max. Recovery (best) - after 75% ERP Rating Heat loss - 24 hours/W Dia x H mm.
1 100 100 Mini RM 5 - 3 kW/1x240V Handwash / 7 ltr. 8 ltr. 7 min. 5 min. C 19 ø200x430
Product Data Sheet
  - click to expand   - click to collapse
Direct Electric Unit Type      
Product Mini RM5      
Produkt No. OSO no. 1 100 100      
Product Capacity Persons Hand-wash      
Product Segment   Domestic      
Product Cost Estimate - Rating - £/££/£££ OSO Standard £      
Weight - Net kg 7      
Height - Max mm. 430      
Diameter mm. 200      
Volume - Actual ltr. 5,5      
v40 ltr. 7,02      
Heat Up - 1 element - 15°C - max Temp. minutes 7      
Heat Up - 2 elements - 15°C - max Temp. minutes -      
Recovery - 1 elements after 75% draw off minutes 5      
Recovery - 2 elements after 75% draw off minutes -      
Thermostat Setting 60      
ERP rating C      
Load profile XXS      
Energy Efficiency % %      
Annual Electricity Consumption Kwh      
Expansion Solution   Integrated      
Dimensions - Cardboard Box LxWxH mm. 225x450x235      
Volume - Cardboard Box 0,06      
Inner Cylinder Stainless Steel Ferritic      
Electric Element(s) Stainless Steel Incoloy 825      
Electric Box and Lid(s) Plastic V0 Plastic      
Insulation PUR Glass wool      
Outer Casing Steel Epoxy Coated      
Energy Source
Type - Primary          
Immersion Heater - Capacity kW 3,0      
Immersion Heater - Phase Phase 1      
Immersion Heater - Voltage Volt 240,0      
Thermostat Type   Surface      
Working Thermostat - Temp. Range °C 30 - 60      
Working Thermostat - Set Temp. °C 45      
Electrical Installation   IEEE regs      
IP Classification   IP 24      
Cold Feed / Balanced Cold / Hot Water mm. 15      
Pressure Reducing Valve   -      
Safety Valve " (inches) 1/2"      
P&T Valve " (inches) -      
Drain Valve " (inches) -      
Secondary Return " (inches) -      
Immersion Heater(s) " (inches) -      
Expansion Vessel   -      
Safety Valve - Opening Pressure +/- 5 % Bar 9      
P&T Valve - Opening Pressure/Temp. Bar/°C -      
Safety Thermostat - Cut-out Temp. °C 85      
Inner Cylinder - Design Pressure /Temp. Bar/°C 10/99      
Certifications / Approvals
Product Certifications Certificates CE / KIWA / WRAS
Manufacturing Plant Approvals Standards ISO 9001:2008 / ISO 14001:2008 / OHSAS 18001
Environmental Declaration 100 % Recyclable / >60 % Recycled Materials / Ozone Depletion Potential of 0 / Global Warming Potential of 1
Warranty - Water Quality EN 98/83EC
Water - Chloride Content Max - Cl ppm 250      
Water - Sulphate Content Max - So4 ppm 250      
Water - Chloride/Sulphate Content Max ppm 250      
Warranty Period - Inner Cylinder / Parts Years 25 / 2