The EHC Comet PV 8kW Electric System Boiler is paired here with a 120-litre Neptune Indirect Unvented Cylinder to form a complete, pre-matched heating and hot water package for smaller UK homes. Both components carry the same EHC brand, which keeps warranty support simple and installation straightforward, with no flue and none of the external pipework a fossil-fuel boiler would demand.
The Comet PV is a multi-output boiler, configurable on-site anywhere between 2kW and 8kW to match the property's actual heat loss rather than over-sizing the appliance. It is built for solar PV integration: a signal from a compatible inverter's export-control relay lets the boiler divert surplus generation into space heating or the cylinder instead of exporting it back to the grid, and the same boiler works equally well as a standard electric system boiler where no PV array is fitted. Weather compensation, a full daily/weekly programmer, and an automatic anti-legionella disinfection cycle are all built into the control panel as standard.
The 120L Neptune cylinder is heated indirectly via the boiler's internal high-efficiency circulating pump through a stainless steel coil, and is topped up by its own 3kW immersion heater for backup or summer-only operation. Because an indirect cylinder recovers hot water faster than a directly-heated immersion-only tank of the same size, this configuration suits properties with a bath or higher daily hot water demand better than a direct cylinder package would.
3 Bar
Cylinder Op. Pressure
24 Months
Boiler Warranty
25 Years
Cylinder Inner Vessel
Important Safety Information: This appliance must be installed by a suitably qualified electrician and, as an unvented hot water cylinder, is a controlled service under Building Regulations — installation must be carried out by a competent person and notified to Local Area Building Control. A magnetic filter must be fitted to the boiler; failure to protect the system in this way will invalidate the manufacturer's warranty.
Please Note: The boiler ships configurable on-site from 2kW up to 8kW via internal DIP switches — the installer sets the rated output to match the property's heat loss calculation. A qualified electrician must confirm the supply cable size and MCB rating against the selected output using the technical data table below.
Good to Know: Full Smart App control of the boiler is available as an option when paired with the separate EHC Internet Module (AHP1004), sold apart from this package.
Solar PV Diversion
A volt-free signal from a compatible PV inverter's export-control relay can trigger the boiler's PV mode, using surplus generation to raise space heating or hot water temperature instead of exporting it to the grid at low value.
On-Site Configurable Output
Internal DIP switches let the installer set the rated boiler power to 2, 4, 6 or 8kW at commissioning, matching the appliance to the building's calculated heat loss rather than fitting a single fixed-output unit.
Weather Compensation
The control panel adjusts the central heating flow temperature automatically against a selectable heating curve and outdoor sensor reading, so the system runs no hotter than the weather demands.
Automatic Anti-Legionella Cycle
A configurable weekly disinfection routine raises the cylinder to a sterilising temperature automatically, reducing the manual oversight a hot water system otherwise needs.
Indirect Coil Recovery
The 120L stainless steel coil is fed by the boiler's own high-efficiency circulating pump, giving faster hot water recovery than an immersion-only direct cylinder of the same capacity.
Smart/Hybrid/Standard Wiring
The boiler can run in full Smart mode from its own control panel, in Hybrid mode alongside third-party room thermostats, or wired as a standard S-Plan heat-only appliance — the same unit adapts to the installation method the site requires.
Built-In Circulating Pump
A high-efficiency pump is integrated into the boiler casing, removing the need for a separate external circulator on the primary heating circuit.
Cascade-Capable Design
Multiple Comet PV boilers can be linked in master/slave cascade for larger heat demands, though this is not required for the single-boiler configuration supplied in this package.
Boiler Performance
Rated Power (Configurable)
2 / 4 / 6 / 8 kW
Rated Voltage
230V 1N~ (single phase)
Outlet Flow Temperature Range
20 – 85 °C
Maximum Water Temperature
100 °C
Maximum Operating Pressure
0.3 MPa (3 bar)
Minimum Operating Pressure
0.05 MPa (0.5 bar)
Built-In Expansion Vessel
~5 litres
Boiler Electrical Data (8kW Setting)
Min. Power Supply Cable Cross-Section
6 mm²
Max. Power Supply Cable Cross-Section
16 mm²
Max. Allowed Network Impedance
0.15 Ω
RCD Protection Required
30 mA
Boiler Construction
Dimensions (H x W x D)
716 x 316 x 235 mm
Boiler Connections
G 3/4" (inside thread)
Safety Class (IP Rating)
IP22
Minimum Flow Rate (up to 8kW)
3.5 l/min
Cylinder — General
Type
Indirect Unvented, Duplex Stainless Steel
Nominal Capacity
120 litres
Casing
Galvanised steel, durable finish
Insulation
CFC/HCFC-free polyurethane foam
Cylinder — Immersion Heater (Backup)
Thread Type
1¾" BSP parallel
Control Thermostat Range
45 °C – 65 °C
Fuse Requirement
13A via double-pole isolating switch
Cylinder — Pressure & Safety
Operating / Maximum Design Pressure
3.0 bar
Maximum Inlet Water Pressure
12.0 bar
Expansion Valve Opening Pressure
6.0 bar
T&P Valve Opening Pressure / Temperature
7.0 bar / 90 °C
Max. Primary Circuit Pressure (Indirect Coil)
3.5 bar
Can this boiler be used without solar PV panels?
Yes. The Comet PV operates as a standard multi-output electric system boiler with no PV array connected. The solar diversion feature is an optional benefit if panels and a compatible inverter are, or later become, part of the installation — it is not a requirement to use the boiler.
Why choose an indirect cylinder instead of a direct one?
An indirect cylinder is heated via the boiler's internal circulating pump through a coil, which recovers hot water faster than an immersion-only direct cylinder of the same size. It suits homes with a bath or higher simultaneous hot water demand, while still including its own 3kW immersion heater as a backup or summer-only heat source.
What is included in this package?
The package includes the EHC Comet PV 8kW boiler and the 120L Neptune indirect unvented cylinder, along with a built-in programmer, room sensor, two 2-port zone valves, a wiring centre, a dual cylinder thermostat, a temperature and pressure relief valve, a 3kW immersion heater, a filling loop, a DHW expansion vessel, a 15mm/22mm tundish, an inlet control set, installation instructions, and a Benchmark logbook.
Does this need a flue?
No. As a fully electric system, the Comet PV boiler produces no combustion by-products and requires no flue, removing that element of installation planning entirely.
What ongoing maintenance does the system need?
The boiler requires an annual service including a magnetic filter clean, expansion vessel pressure check (1.5 bar), and electrical connection checks. The unvented cylinder also requires annual servicing — testing both safety valves, checking the expansion vessel pressure (3 bar), and confirming immersion heater operation — to keep the 25-year cylinder guarantee valid.
Can the boiler's output be changed after installation?
The rated power is set via internal DIP switches during commissioning to match the property's heat loss. Changing it afterwards is possible but must be carried out by a qualified electrician, who will also need to reconfirm the supply cable and MCB rating are suitable for the new setting.
