Instant Hot Water99.7% Efficient4.8–9.6 kWUp to 5.5 l/minA4-Sized — 315×210×120mmIP44240V Single Phase10 Bar20–60°C Temperature ControlNo Scaling / No BurnoutDual-Unit Tandem Option5-Year Warranty
The ThermoSphere Micro Electric Boiler (MEB) is an instant hot water heater and heating boiler that delivers a continuous flow of hot water at up to 60°C with 99.7% efficiency — with no cylinder, no expansion vessel and no immersion element. A patented direct energy transfer system heats the water as it flows through the unit, adjusting power output 100 times per second to maintain the exact set temperature regardless of flow rate changes — eliminating the temperature spikes and fluctuations common with conventional instantaneous heaters. Available in five output variants from 4.8 kW to 9.6 kW, with the option to install two units in tandem for up to 11 l/min combined flow. At just 315 × 210 × 120mm — the footprint of an A4 sheet of paper — it fits under sinks, in airing cupboards, loft spaces and service voids where no other water heating solution would be practical. Suitable for domestic hot water, wet UFH, solar thermal top-up and care home temperature limiting.
99.7%
Efficiency
5.5 l/m
Max Flow (single)
11 l/m
Max Flow (tandem)
60°C
Max Temperature
10 bar
Max Pressure
5 yr
Warranty
ℹ Choosing Your Model: Use the variant table below to select the right output. The key figure is your outlet flow rate in litres per minute — measure it with a 1-litre jug and a stopwatch. Match this to the flow column at +25°C temperature rise. Most UK homes with a shower will need the TSMEB-9 (9.6 kW), the most popular model. If in doubt, size up rather than down.
Select Your Variant — Single & Dual Installation
Model
Max Output
Flow (+25°C)
MCB / Current
Supply Cable
Best For
TSMEB-4
4.8 kW
2.8 l/min
20A
2.5 mm²
Lowest output — suited to hand basins and modest kitchen taps where very low flow rates (under 2.5 l/min) are typical.
TSMEB-6
6.0 kW
3.4 l/min
25A
4.0 mm²
Good match for a single kitchen tap or cloakroom basin in a home with moderate mains pressure.
TSMEB-7
7.2 kW
4.1 l/min
30A
4.0 mm²
Mid-range choice — handles a single shower at typical UK shower head flow rates (3.5–4 l/min).
TSMEB-8
8.4 kW
4.8 l/min
35A
6.0 mm²
Comfortable single-shower option with headroom; also suitable for kitchen applications with higher flow rates.
TSMEB-9 ★
9.6 kW
5.5 l/min
40A
6.0 mm²
Most popular model. Maximum single-unit output — up to 5.5 l/min at a 25°C temperature rise.
★ Most popular model. All models: 240V, single phase. MCB ratings above are maximum load — install RCBO for circuit protection.
Dual / Tandem Installation (two units in parallel)
Tandem Pair
Combined Output
Combined Flow
MCB per unit
Cable per unit
TSMEB-4 ×2
9.6 kW
5.6 l/min
20A each
2.5 mm² each
TSMEB-6 ×2
12.0 kW
6.8 l/min
25A each
4.0 mm² each
TSMEB-7 ×2
14.4 kW
8.2 l/min
30A each
4.0 mm² each
TSMEB-8 ×2
16.8 kW
9.6 l/min
35A each
6.0 mm² each
TSMEB-9 ×2
19.2 kW
11.0 l/min
40A each
6.0 mm² each
Each unit in a tandem pair requires its own dedicated supply circuit and RCBO.
Applications
🚿
Domestic Hot Water — Showers & Taps
Instant hot water at the tap or showerhead. The digital temperature control prevents scalding; particularly suited to care homes and assisted-living environments where water temperature must be limited to 43°C.
☀️
Solar Thermal & Heat Pump Top-Up
Acts as a 100%-efficient electric top-up when solar or heat pump output falls short — for example, on overcast days or during high demand. The heat pump runs at its optimum set point; the MEB handles the temperature shortfall.
🔥
Wet Underfloor Heating
Delivers water at the exact flow temperature required for UFH circuits — no mixing valve or buffer tank needed. Particularly useful in retrofit single-room UFH where running full heating pipework is impractical.
🏥
Temperature Limiting — Care & Commercial
Precise digital temperature limiting makes the MEB ideal for care homes, schools and commercial premises where safe hot water temperatures must be maintained consistently across all outlets.
✅ No Cylinder, No Expansion Vessel: Unlike unvented cylinders, the MEB needs only a 5 bar pressure-limiting valve and an isolating stop valve on the cold supply. Water connection is ½" BSP. Typical installation time: half a day for a qualified plumber/electrician working together.
Key Features & Technology
Patented Direct Energy Transfer — No Element, No Scale, No Burnout
The Micro Electric Boiler uses a patented direct energy transfer heating system — not a resistive wire element or immersion heater. Energy is transferred directly into the water as it flows through the unit, making it impossible to overheat, burn out or scale in the way that conventional instantaneous heaters do. There is no heating element surface that can calcify, no hot spot that can burn out, and no thermal runaway risk.
Intelligent Power Adjustment — 100 Times Per Second
An on-board microprocessor measures incoming water temperature and flow rate and adjusts power output 100 times per second to deliver the set outlet temperature regardless of changes in flow or incoming temperature. Turn on a second tap, flush a toilet — the MEB compensates instantly and the shower temperature does not spike or drop. This eliminates the temperature fluctuation that affects conventional instantaneous heaters and electric showers.
Double the Flow Rate of Conventional Instantaneous Heaters
Most instantaneous electric water heaters achieve 2.5–3 l/min at a 25°C temperature rise. The MEB delivers up to 5.5 l/min on a single unit — roughly double. For installations needing more, two units installed in tandem give up to 11 l/min — enough for a bath fill or simultaneous multi-outlet demand. Each unit in a tandem pair runs on its own dedicated circuit.
A4 Footprint — 315 × 210 × 120mm — Fits Anywhere
The MEB occupies roughly the space of a sheet of A4 paper on the wall at just 315mm tall × 210mm wide × 120mm deep, with a nominal water capacity of 385 ml. It installs directly to any wall surface using the included fixing plate, making it practical for under-sink kitchen cupboards, airing cupboards, service voids and loft spaces — wherever a cylinder or unvented unit would be impossible to accommodate.
20–60°C Digital Temperature Selection
Outlet temperature is set digitally from 20°C to 60°C in precise increments via the on-unit display. This makes the MEB particularly suitable for care homes, schools and shared accommodation where a safe maximum must be enforced — typically 43°C for care home hot water outlets — without relying on a thermostatic mixing valve.
No Expansion Vessel Required — Simplified Installation
Unlike unvented cylinders, the MEB does not require an expansion vessel. The incoming cold water supply needs only a 5 bar pressure-limiting valve and an isolating stop valve. Water connection is via a ½" BSP fitting. This dramatically reduces installation time and pipework — typically a half-day installation for a qualified electrician/plumber.
Activates at 1.5 l/min — Low Flow Rate Start
The MEB switches on automatically when flow rate reaches 1.5 litres per minute and switches off when flow stops. No manual switching required. The 385ml nominal water capacity means only a small volume of cool water is displaced at the start of a draw — hot water arrives at the outlet almost immediately after opening the tap.
5-Year Warranty — Made in the UK
ThermoSphere designs and manufactures in the UK. The MEB carries a 5-year product warranty. ThermoSphere provides installer technical support directly, including on-site commissioning assistance and a zero-callback guarantee for registered installers once the system is correctly commissioned.
★ Most popular model. All models 240V / single phase. Each model requires a dedicated circuit.
ℹ Installation: Fit a 5 bar pressure-limiting valve and isolating stop valve on the cold water inlet. Install an RCBO (not just an MCB) to protect the dedicated circuit. For a tandem installation, each unit requires its own independent circuit and RCBO. The MEB must be installed and commissioned by a qualified electrician and plumber. Technical support and commissioning assistance is available directly from ThermoSphere.
Frequently Asked Questions
Which model (TSMEB-4 to TSMEB-9) should I choose?
The answer depends on your typical outlet flow rate and incoming cold water temperature. Test your flow rate with a 1-litre measuring jug and stopwatch. The TSMEB-9 (9.6 kW) is the most popular model and is the right choice for most UK homes where the outlet flow rate reaches 4–5.5 l/min. If your flow rate is lower (e.g. a restricted hand basin), a TSMEB-6 or TSMEB-7 may be sufficient. If you need higher flow rates than any single unit can provide, two units installed in tandem give up to 11 l/min. The variant table on this page lists the maximum flow rate at a +25°C temperature rise for each model.
What electrical supply does the MEB need?
Each model requires a dedicated single-phase 240V circuit with an RCBO for circuit protection. The required MCB/RCBO rating and cable size depend on the model chosen: TSMEB-4 needs 20A / 2.5mm²; TSMEB-6 needs 25A / 4mm²; TSMEB-7 needs 30A / 4mm²; TSMEB-8 needs 35A / 6mm²; TSMEB-9 needs 40A / 6mm². Always have cable and MCB sizing confirmed by a qualified electrician before ordering. A tandem installation requires two separate dedicated circuits, one per unit.
Does the MEB replace a hot water cylinder entirely?
For domestic hot water (DHW) applications, yes — the MEB is an instantaneous heater and requires no storage cylinder. Cold water enters, is heated on demand, and exits at the set temperature. No expansion vessel, no immersion heater, no cylinder. For heating system applications (e.g. UFH flow temperature), the MEB acts as the heat source in place of a boiler, again with no buffer tank required in most cases.
Can it be used as a solar thermal or heat pump top-up?
Yes — this is one of the most efficient use cases. Set your heat pump or solar thermal system to run at its optimum flow temperature for efficiency. The MEB is installed downstream and tops up to the desired outlet temperature using only the precise amount of electrical energy needed. Because the MEB is nearly 100% efficient and only operates when there is a shortfall, running costs in this configuration are typically very low.
Is there any risk of scaling or limescale build-up?
No. Because the MEB uses direct energy transfer rather than a heating element, there is no hot surface for limescale to deposit on. Conventional instantaneous heaters and immersion elements develop a calcified coating over time that reduces efficiency and eventually causes burnout — the MEB is immune to this failure mode. This makes it particularly suitable for hard-water areas without any additional treatment.
Related Products
ThermoSphere Electric Combi Boiler
Full central heating + DHW — for properties with radiators
Wet Underfloor Heating Kits
Paired perfectly with the MEB as a compact UFH heat source
DAB VS Bronze Circulating Pump
Sanitary hot water circulation for DHWS loops
BTU & WATT Calculator
Room Dimensions
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)
Required Heating
0
Watts
0
BTUs
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