The ThermoSphere Electric System Boiler is a slimline, wall-mounted electric flow boiler with an integrated circulation pump, built for central heating in properties without a mains gas supply. Available in outputs from 4.5kW to 24kW, it suits everything from small flats to larger commercial spaces, running on either a single-phase (230V) or three-phase (400V) electrical supply.
With 3-stage heating elements for modulated output and no flue, gas connection or annual servicing requirement, it's a straightforward retrofit for radiator or wet underfloor heating systems, and integrates with indirect unvented cylinders for hot water.
2 bar
Max System Pressure
100%
Electric-to-Heat Efficiency
Electrical Supply Requirement
Models up to and including 15kW are fitted with a jumper pin, allowing single-phase (230V) connection out of the box; removing the jumper and wiring each live phase separately enables three-phase (400V) operation. 18kW models and above are designed for three-phase supply only. Always confirm supply capacity with a qualified electrician before specifying.
No Flue or Gas Supply Needed
Runs on 100% electric operation with zero on-site emissions, making it a straightforward option for off-grid properties or all-electric new builds without the need for flue routing or gas safety certification.
Single or Three-Phase Flexibility
Connects to either a 230V single-phase or 400V three-phase supply depending on model and site electrical capacity, with a jumper-pin arrangement simplifying single-phase wiring on smaller models.
3-Stage Heating Elements
Multi-stage element modulation improves comfort and electrical load management compared with a simple on/off single-element design, reducing peak demand spikes.
Integrated Circulation Pump
Unlike the heat-only variant, this system boiler includes a built-in circulation pump, simplifying the installation kit needed for radiator or underfloor heating circuits.
Compatible With Indirect Cylinders
Pairs with indirect unvented hot water cylinders for domestic hot water, alongside radiator or wet underfloor heating circuits on the same appliance.
Smart Control Ready
Compatible with thermostats, programmers and smart heating controls, allowing zoned or scheduled operation on top of the boiler's own safety cut-outs.
| Model |
Power Output |
Voltage |
Max Current |
Dimensions (H x W x D) |
Weight |
| TSEFB-P4.5 |
4.5 kW |
230/400V |
≈21 A |
755 x 215 x 150mm |
14kg |
| TSEFB-P6 |
6.0 kW |
230/400V |
≈27 A |
755 x 215 x 150mm |
14kg |
| TSEFB-P9 |
9.0 kW |
230/400V |
≈40 A |
755 x 215 x 150mm |
14kg |
| TSEFB-P12 |
12.0 kW |
230/400V |
≈53 A |
755 x 215 x 150mm |
14kg |
| TSEFB-P15 |
15.0 kW |
400V (3-phase) |
≈22 A per phase |
755 x 215 x 150mm |
15kg |
| TSEFB-P18 |
18.0 kW |
400V (3-phase only) |
≈26 A per phase |
755 x 215 x 150mm |
15kg |
| TSEFB-P24 |
24.0 kW |
400V (3-phase only) |
≈35 A per phase |
755 x 215 x 150mm |
15kg |
| Performance |
| Output Range |
4.5kW to 24kW |
| Efficiency |
100% electric-to-heat conversion (no flue losses) |
| Efficiency Class |
D |
| Max Flow Temperature |
65°C |
| Electrical & Pressure |
| Voltage |
230/400V (single or three-phase, model dependent) |
| Max System Pressure |
2.0 bar (unit); 3 bar per manufacturer datasheet |
| Protection Rating |
IP22 |
| IEC Protection Class |
Class I |
| Included Components |
| Circulation Pump |
Integrated |
| Expansion Vessel |
7 litre (spec varies with model size) |
| Safety Features |
High-limit thermostat, low water protection, pressure relief valve, overheat cut-out |
| Compliance |
| Regulatory Compliance |
ErP Lot20, UK electrical installation standards |
| Warranty |
2–5 years depending on registration and installer |
Can this boiler run on a standard domestic single-phase supply?
Yes, for models up to and including 15kW. These ship with a jumper pin joining the three live terminals for single-phase (230V) connection. Models of 18kW and above require a three-phase (400V) supply.
How do I size the right output for my property?
A rough guide is to allow 1.5kW per radiator, so 4 radiators would suggest a 6kW boiler and 6 radiators would suggest a 9kW unit. Ceiling height, insulation standard and glazing type also affect the real-world demand, so a full heat loss calculation is recommended for larger properties.
Does this model include a pump?
Yes — this is the System Boiler variant with an integrated circulation pump, as distinct from ThermoSphere's Heat Only Boiler which is supplied without a pump for systems where one is already present.
Can it heat both radiators and a hot water cylinder?
Yes, the system boiler is compatible with wet underfloor heating and radiator circuits, and can be paired with an indirect unvented cylinder to provide domestic hot water alongside space heating.
What ongoing maintenance does it need?
Electric boilers have no combustion process, flue, or annual gas safety inspection requirement, which significantly reduces routine maintenance and callout costs compared with a gas system boiler.
