The ThermoSphere Electric Heat Only Boiler is a wall-mounted electric boiler designed to heat water for central heating radiators, wet underfloor heating circuits, and domestic hot water via an indirect cylinder coil. Built around a cluster of resistive heating elements housed in an insulated steel cylinder, it delivers a 99.8% efficient heat source with no flue gas emissions and no fossil fuel burned on site.
It is the natural alternative to a gas or oil boiler for properties without a gas supply, or where flue routing and space are at a premium. The range spans 4.5kW to 15kW across five models, all sharing the same compact wall-mounted casing, plumbing layout and control logic — so sizing is simply a matter of matching output to heating/hot water demand.
Good to Know
Works with standard radiators, programmers, thermostats and thermostatic radiator valves, and can be plumbed into an indirect hot water cylinder to provide domestic hot water alongside space heating — making it a straightforward drop-in for existing wet heating systems.
Important Safety Information
This appliance must only be installed and maintained by a qualified, competent professional. It must be safely earthed at all times, fed from a dedicated, suitably rated supply circuit with provision for safe electrical isolation, and the boiler must never be energised before the plumbing circuit is filled and pressurised. Models up to and including 12kW can run on single-phase (230V) or three-phase (400V) supply; the 15kW model is three-phase (400V) only.
Zero On-Site Emissions
With 99.8% efficiency and no flue gas emissions, the boiler removes the need for any flue routing, making it ideal for flats, outbuildings or renovations where running a flue is impractical or impossible.
Resistive Element Cluster Design
Heat is generated by a cluster of resistive heating elements housed inside an insulated steel cylinder, with cold water entering at the base and heated water leaving via the top flow connection.
Single or Three-Phase Flexibility
Models from 4.5kW to 12kW can be wired for single-phase (230V) or three-phase (400V) supply by removing a jumper clip on the live terminals, giving installers flexibility based on the property's existing supply.
Built-In Control Circuit Supply
A 3 Amp fused control circuit supply is built into the boiler, removing the need for a separate fused spur when wiring in external thermostats or programmers.
Dual Safety Cut-Out Protection
A thermal cut-out switch isolates the heating elements above 80°C, while the internal 3 Amp control circuit fuse protects the low-voltage control wiring.
Compact Wall-Mounted Footprint
At just 220mm × 575mm × 115mm, the boiler mounts directly to a load-bearing wall with 500mm clearance recommended on all sides for safe access and servicing.
| General |
| Dimensions (W×H×D) |
220mm × 575mm × 115mm |
| Max working temperature |
65°C |
| Max working pressure |
2.0 BAR (rated system pressure 0.5-2 BAR; 1.5 BAR recommended) |
| Protection rating |
IP22 |
| IEC protection |
Class I |
| Efficiency |
99.8%, zero flue gas emissions |
| Warranty |
5 years |
| Safety & Control |
| Thermal cut-out |
Isolates elements above 80°C |
| Control circuit fuse |
Internal 3 Amp fuse |
| Control circuit supply |
3 Amp, built-in (no separate fused spur required) |
| Compatible controls |
External room/cylinder thermostats, programmers, TRVs, S Plan/Y Plan |
| Plumbing connections |
3/4" BSP flow and return |
| Earthing |
Must be permanently earthed to mains earth |
| Code |
Output |
Output per Element |
Voltage |
Current |
Weight |
EAN |
| TSEFB-4.5 |
4.5kW |
1.5kW |
230/400V |
21A |
13kg |
5056257307954 |
| TSEFB-6 |
6.0kW |
2.0kW |
230/400V |
27A |
13kg |
5056257307961 |
| TSEFB-9 |
9.0kW |
3.0kW |
230/400V |
40A |
13kg |
5056257307978 |
| TSEFB-12 |
12.0kW |
4.0kW |
230/400V |
53A |
13kg |
5056257307985 |
| TSEFB-15 |
15.0kW |
5.0kW |
400V |
22A |
13kg |
5056257307992 |
The manufacturer's data sheet lists maximum working pressure as 2.0 BAR, while the installation manual states the safe operating range as 0.5-2 BAR, with 1.5 BAR recommended.
Can this boiler provide domestic hot water as well as heating?
Yes. When plumbed into an indirect hot water storage cylinder, the boiler can provide both central heating and domestic hot water from the same unit.
Does the 15kW model work on a single-phase supply?
No. The TSEFB-15 is 400V three-phase only. Models from 4.5kW to 12kW can run on either single-phase (230V) or three-phase (400V) supply.
Do I need a separate fused spur for room thermostats or programmers?
No. The boiler includes a built-in 3 Amp fused control circuit supply, so external controls can be powered directly from the boiler.
What size circuit breaker do I need?
The circuit breaker must be rated higher than the maximum current draw of the chosen model — for example, a boiler drawing 21A should be protected by at minimum a 25A MCB. Always confirm sizing with a qualified electrician.
Can this boiler be installed without a flue?
Yes. As an electric resistive-element boiler, it produces no flue gases and requires no flue, making it suitable for properties without gas or where flue routing isn't possible.
What is the warranty on this boiler?
Each unit carries a 5-year warranty from Thermogroup Ltd, subject to installation by a qualified professional in accordance with the ThermoSphere instructions.
