Elterm Electric Heat Only Electric Boiler

Description

The Elterm Sergeant (AsBN) is a heat-only electric boiler built for wet central heating systems that have no mains gas connection, or that need a compact, flue-free heat source. It connects directly into radiator or underfloor heating circuits, working as the sole heat source in off-grid properties or as an alternative, supporting, or temporary heat source alongside a gas boiler or heat pump.

Manufactured in Poland by Elterm, a heating specialist with over 30 years of production experience, the Sergeant uses Basic LED automation and is available across a wide power range from 4kW to 24kW, with power-splitting electronics that let a single unit modulate down to serve smaller heat loads. An optional DHW package (electrovalve, cylinder sensor and activation code) can be added to give the Sergeant priority control over a separate hot water cylinder, effectively turning it into a system boiler.

4-24kW

Power range

99.5%

Boiler efficiency

Class D

Energy efficiency (A+++ to D scale)

24 months

Manufacturer guarantee

70°C

Max CH operating temperature

IP-rated

Wall-mounted, flue-free design

Installation & Electrical Safety

Electrical and hydraulic assembly, commissioning and maintenance must be carried out by a qualified, legally authorised installer. Adequate overcurrent and residual current (RCD) protection is mandatory, sized to the fuse and cable ratings in the spec table below. Elterm's warranty does not cover damage caused by incorrect electrical or hydraulic connection.

Wide Power Range

Six output versions from 6kW to 24kW, plus a 4kW single-phase entry point, so the correct size can be matched to the building's heat loss rather than over- or under-sizing the system.

PV Ready Functionality

Includes 4x PV-ready features: an operation counter, adjustable maximum power lock, a voltage-free (0V) contact for external control, and a disconnectable contact that switches off a second heat source when the boiler is running — useful where solar generation is variable.

Power Modulation

Larger models (15kW, 18kW, 24kW) can be manually or electronically split into lower output stages (e.g. 18kW modulates to 12/6/4kW), reducing running costs and allowing gentler cycling on partially loaded systems.

Sealed or Open Vented

Works in both sealed and open-vented (air-vented) central heating systems, giving flexibility for retrofits into older systems as well as new sealed installations.

Built-in Safety Systems

Equipped with quadruple overheat protection (OSC), a switching-frequency protection system (SC), a Watch Dog processor monitor, and an Anti-Stop pump function that exercises the pump for one minute every 14 days to prevent seizure.

Heat Pump Compatible

Can be dedicated to cooperate with heat pumps, acting as a backup or peak-demand top-up source, with an operation counter that can trigger a secondary heat source once a set energy threshold is reached.

Technical Specification — Elterm Sergeant (AsBN)

Model codes

123006 / 123009 / 123012 / 123015 / 123018 / 123024

Power outputs

6kW · 9kW · 12kW · 15kW · 18kW · 24kW

Electrical supply

6kW & 9kW available in 230V single-phase or 400V 3-phase; 12kW-24kW require 400V 3-phase

Automation

Basic LED control panel

Energy efficiency class

D (ErP scale spans A+++ to D)

Boiler efficiency

99.5%

Max CH operating temperature

70°C

Hysteresis range

1-6°C, adjustable

PID heating dynamics

5-step adjustable, factory setting 3

Connections

¾" external (CH flow/return)

Built-in equipment

Expansion vessel, circulation pump, safety valve, air vent, pressure gauge (15kW-24kW models)

Optional DHW package

Electrovalve, cylinder sensor, activation code (min. 12kW coil cylinder required)

Anti-Stop pump protection

Runs pump for 1 minute every 14 days when boiler is OFF

Standards compliance

LVD, RoHS, EMC, WEEE, ErP directives

Manufacturer guarantee

24 months from installation date, subject to registered commissioning

Electrical Protection by Power Output

4kW (1-phase)

1 x 20A fuse, 3 x 4mm² cable

4kW (2-phase)

2 x 10A fuse, 5 x 2.5mm² cable

6kW (1-phase)

1 x 32A fuse, 3 x 4mm² cable

6kW (3-phase)

3 x 10A fuse, 5 x 2.5mm² cable

9kW (3-phase)

3 x 16A fuse, 5 x 2.5mm² cable

12kW (3-phase)

3 x 20A fuse, 5 x 4mm² cable

15kW (3-phase)

3 x 25A fuse, 5 x 4mm² cable

18kW (3-phase)

3 x 32A fuse, 5 x 6mm² cable

24kW (3-phase)

3 x 40A fuse, 5 x 10mm² cable

Model

Power

Supply

Modulation Steps

Sergeant 6/4kW

6kW

230V or 400V

6 = 2+2+2kW · 4 = 2+2kW

Sergeant 9kW

9kW

230V or 400V

3 x 3kW stages

Sergeant 12kW

12kW

400V

3 x 4kW stages

Sergeant 15/9/6/4kW

15kW

400V

15/9/6/4kW selectable

Sergeant 18/12/6/4kW

18kW

400V

18/12/6/4kW selectable

Sergeant 24/12kW

24kW

400V

24/12kW selectable

Is the Sergeant boiler suitable for a property with no gas supply?

Yes. The Sergeant is designed as a standalone heat-only electric boiler for wet central heating systems in properties without mains gas, and it can also serve as an alternative or backup heat source alongside an existing gas boiler or heat pump.

Can this boiler heat domestic hot water as well as radiators?

Not on its own. The Sergeant is a heat-only boiler for central heating circuits. Domestic hot water can be added by fitting the optional DHW package together with a separate cylinder with a minimum 12kW coil, which lets the boiler prioritise heating the cylinder on demand.

What electrical supply does the Sergeant need?

It depends on the power output. The 6kW and 9kW versions are available in either 230V single-phase or 400V 3-phase; the 12kW, 15kW, 18kW and 24kW versions require a 400V 3-phase supply. Always confirm the exact fuse and cable size with a qualified electrician using the protection table above.

Does the Sergeant work with solar PV?

Yes. It includes 4x PV-ready functionality, including a maximum power lock that can be set to match available solar generation, and a built-in energy meter to help it cooperate with a PV installation.

Can the boiler's power output be reduced after installation?

On the 15kW, 18kW and 24kW models, yes — output can be manually or electronically modulated down to lower stages (for example, 18kW down to 12kW, 6kW or 4kW) via the control panel, which is useful where the building's heat loss is lower than the installed capacity.

BTU Calculator

BTU & WATT Calculator

Room Dimensions

Length (in m):

Width (in m):

Height (in m):

Room Type

Living Room

Bedroom

Kitchen

Bathroom

Conservatory

Hallway

Glazing Type

Single Glazed

Double Glazed

Triple Glazed

External Walls

0 Wall

1 Wall

2 Walls

3 Walls

4 Walls

Insulation Level

Poor

Average

Good (New Build)

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Required Heating

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Watts

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