The OSO Standard Immersion Heater (product code 8015192) is a genuine OSO Hotwater replacement immersion element rated 3kW at 240V, fitted with a built-in working thermostat as standard. It uses OSO's non-standard 1-1/4" boss, so a 50mm box spanner is recommended for installation rather than a standard immersion spanner.
This is a direct replacement for the earlier OSO codes 71259 and 71255, and is compatible across the majority of the OSO Hotwater cylinder range, including the 20 Series, 16 Series, Twincoil, Solarcyl, Ecoline, and Geo ranges.
1-1/4"
Boss Size (Non-Standard)
Please Note: OSO immersion heaters use a non-standard 1-1/4" boss, unlike the more common 2-1/4" BSP boss found on most UK domestic cylinders. A 50mm box spanner is recommended for installation and removal — a standard immersion spanner will not fit.
Built-In Working Thermostat
Unlike the rod/smart-thermostat variant, this heater is supplied with its thermostat factory-fitted internally, adjustable between 40°C and 70°C, with no separate thermostat to source or fit.
Integrated Safety Cut-Out
A safety cut-out is built into the thermostat assembly and operates at 85°C ±3°C, protecting the cylinder against overheating independently of the main temperature control.
Direct Replacement for Earlier OSO Codes
This part directly replaces OSO codes 71259 and 71255, making it a straightforward like-for-like replacement on older OSO cylinders still fitted with those earlier elements.
Wide OSO Cylinder Compatibility
Confirmed compatible with the 20 Series, 16 Series, Twincoil, Solarcyl, Ecoline and Geo200/250/300 ranges, plus specific 20RI/20RD combination models (20RI250F1, 20RI300F1, 20RI380F1, 20RI200TC, 20RI250TC, 20RI399TC, and more).
Factory-Mounted Internal Wiring
All internal wiring on the OSO immersion assembly is factory mounted, simplifying installation and reducing on-site wiring error.
Economy 7 Compatible
Where a cylinder has upper and lower immersion positions, the lower heater can be run on an off-peak tariff while the upper heater runs on the day tariff, connected via a suitable water heater controller.
| General Specification |
| Manufacturer |
OSO Hotwater (UK) Limited |
| OSO Product Code |
8015192 |
| Replaces |
71259, 71255 |
| Power Rating |
3kW @ 240V |
| Boss Size |
1-1/4" (non-standard OSO boss) |
| Thermostat Type |
Built-in, factory-fitted |
| Thermostat Range |
40°C to 70°C, adjustable |
| Safety Cut-Out |
85°C ±3°C, integrated within the thermostat |
| Recommended Tool |
50mm box spanner |
| Electrical Connection |
Double-pole linked switch, minimum break capacity 13A |
| Cylinder Compatibility |
| Series |
20 Series, 16 Series, Twincoil |
| Specific Models |
20RI250F1, 20RI300F1, 20RI380F1, 20RI200TC, 20RI250TC, 20RI399TC, 20RI380TC, 20RI250SD, 20RI300SD |
| Other Ranges |
GEO200, GEO250, GEO300, Solarcyl, Ecoline |
Important Safety Information: This is a mains-voltage electrical heating product for installation into a water-filled cylinder. Installation, wiring and testing must be carried out by a suitably qualified electrician or a Part P registered competent person, in accordance with current IEE wiring regulations (BS 7671). The appliance must be permanently connected to the electrical supply through a double-pole linked switch with a minimum break capacity of 13A. The heater must never be switched on unless fully immersed in water.
Does this heater come with a thermostat already fitted?
Yes. This variant (8015192) has a built-in working thermostat, adjustable between 40°C and 70°C, already factory-fitted — there is no separate thermostat to buy or install.
What size spanner do I need to fit or remove this heater?
OSO immersion heaters use a non-standard 1-1/4" boss. A 50mm box spanner is recommended, as a standard immersion spanner will not fit this boss size.
Which OSO cylinders is this heater compatible with?
It is compatible with the 20 Series, 16 Series, Twincoil, Solarcyl and Ecoline ranges, the GEO200/250/300 models, and specific 20RI/20RD combination models including 20RI250F1, 20RI300F1 and 20RI380F1.
Is this a direct replacement for my older OSO immersion heater?
Yes, if your existing heater is coded 71259 or 71255, this part (8015192) is the current direct replacement.
What happens if the safety cut-out trips?
The integrated safety cut-out operates at 85°C ±3°C. Before resetting it or adjusting the thermostat setting, always isolate the electrical supply to the unit first, in line with the manufacturer's installation instructions.
