The MAXI series is our class-leading commercial range of hot water calorifiers; built to the high standards of design and efficiency that is synonymous with OSO Hotwater products. The MAXI range has been manufactured with EVERLAST™ high-alloy stainless steel in combination with ULTRAWELD™ technology for optimal corrosion resistance. Not only is the MAXI range extremely efficient, with industry-leading performance it can also be modified according to customer requirements.

The MAXI GEOCOIL— MGC has been custom-made for maximum hot water production from heat pumps up to 40 kW (400 L = 25 kW / 600 / 1 000 L = 40 kW); with a large surface area; smooth-piped and scaleesistant heating coil. The units are also suitable for solar collectors up to 40 m². MAXI GEOCOIL has ultra-grade INCOTEC immersion heaters acting as a booster above the heating coil. This feature raises the temperature to increase capacity and prevent bacterial growth. The booster heaters also provide maximum safety if there are any operational problems with the energy source. The electric immersion heaters will raise the temperature to a higher level and are available from 5 to 15 kW, in single or three phase 230 or 400V . They are thermostat controlled with separate safety thermal cutout. Contactors are not required and the supply cable is connected directly to the thermostat assembly.

G3 Kits and expansion vessel include

Other sizes and specifications are available to order.

• Highly efficient DHW production from heat pump up to 40 kW
• Extreme operational safety with electric heater as booster / back-up
• 10 bar design pressure and class-leading corrosion resistance


NANOPUR – Class-leading insulation (300/400 L)
ISOFLEX+VIP – Class-leading insulation (600/1000 L)
ULTRAWELD – Superior corrosion resistance
INCOTEC – High durability in hard water
MAXTEMP – Solar / hot water connection
ECO-HOTWATER – DHW from alternative energy


Mixing valve – See separate commercial add-ons
Thermostat – Adjustable 60-90°C – Preset 75°C
Safety valve – TP 9 bar/99°C – 3/4” to drain
Flow/ret. conn. – 2 x 1-½” female BSP threads
Coil connection – 400 L.: 2 x ¾” female BSP threads
600-1000 L.: – 2 x 1” female BSP threads
Other connections – 4 x ¾” female BSP threads


OSO Hotwater UK product brochure

Manual Maxi Geocoil MGC 400 l.
Manual Maxi Geocoil MGC 600-10 000 l.