The Strom 9kW Single Phase Heat Only Electric Boiler delivers reliable central heating without the bulk — a compact, wall-mounted unit purpose-built for properties where space is at a premium or where built-in pumps and expansion vessels simply aren't needed. With zero carbon monoxide emissions, near-silent operation and a patented serpentine heat exchanger, this is the clean, quiet alternative to gas that fits almost anywhere in your home. 9kW Heat Output 100% Efficient 41A Draw @ 230VAC 2 Yr Warranty (registered) 520mm Height ⚠ Professional Installation RequiredThis boiler must be installed by a qualified electrician who is a member of a competent persons scheme. A Part P electrical certificate and notification under Building Regulations are legally required. The heating circuits must also be designed and commissioned by a competent plumber or heating engineer. ℹ Heat Only Boiler — External Components NeededUnlike a system boiler, the Heat Only variant has no built-in pump, expansion vessel or pressure relief valve. You will need to supply and fit: circulating pump, expansion vessel & kit, pressure gauge, automatic bypass valve, isolation valves, and external heating controls (programmer + room thermostat or programmable thermostat). KEY FEATURES ♻ Patented Serpentine Heat Exchanger Strom's unique heat exchanger distributes heat evenly across the entire element surface, eliminating hot spots that cause limescale and corrosion. The result is a longer-lasting element and consistently efficient heat transfer. 🔅 Near-Silent, Zero-Emission Operation With no combustion, no flue and no carbon monoxide, this boiler can be installed in virtually any room. Minimal moving parts mean whisper-quiet performance day and night. 🔍 Compact Form Factor At just 520 × 235 × 120 mm, the unit is considerably smaller than a conventional boiler. Wall-mounted via an integrated bracket with supplied expanding bolts, it fits neatly in cupboards, utility rooms or airing cupboards. ⚡ 100% Electrical Efficiency Every kilowatt drawn from the supply converts directly to heat — no flue losses, no standby pilot flame. Pair with a green electricity tariff or your own solar panels to reduce running costs further. ☀ Frost Protection Built-In An onboard frost-protection mode activates automatically to safeguard the boiler and pipework in unheated spaces. For external outbuildings, Strom recommends adding an external frost stat wired inline. 🔌 Modular & Serviceable Design The fully modular component layout means individual parts can be replaced without swapping the whole unit, keeping long-term maintenance costs low. The heating element is a single replaceable assembly — straightforward for any qualified engineer. ☹ External Thermostat Compatible A dedicated switch-live thermostat terminal on the PCB accepts any standard room thermostat or programmable thermostat, giving you full flexibility over how your heating schedule is managed. ☉ Solar-Ready & Off-Grid Ideal Compatible with solar PV divert systems (e.g. via an immersion controller), making this boiler an excellent companion to on-site generation. It's also the go-to choice for properties not connected to the gas network. TECHNICAL SPECIFICATIONS Heat Output 9 kW Phase Single Phase (230 VAC) Current Draw @ 230 VAC 41 A Minimum MCB / RCB Breaker 45 A Minimum Cable Size 6 mm² Heating Temperature Range 20 °C – 80 °C Heating Pressure Range 0.5 – 1.5 Bar Heating Flow & Return Connection ¾" Male BSP (flexi hoses or push-fit irons recommended) PRV Connection Size 15 mm Compression Dimensions (H × W × D) 520 × 235 × 120 mm ERP Rating (Heating) D Warranty 2 years when registered within 45 days of purchase (1 year if unregistered) Compliance BS EN 12828, BS EN 12831, BS EN 14336, BS7671 (IEE 19th Ed), BS EN 7593, Part L 2022 What's in the Box Heat Only Boiler, integrated wall mounting bracket, 3× expanding wall bolts, wall mounting guide, installation manual FREQUENTLY ASKED QUESTIONS What is a Heat Only boiler and how does it differ from a System boiler? A Heat Only boiler (also called an Open Vent or Regular boiler) provides only the heat source — it has no built-in circulating pump, expansion vessel, pressure gauge or pressure relief valve. Those components are fitted externally by your installer. This makes the unit physically smaller and is ideal for situations where you already have a pump and vessel arrangement, or where you need more flexibility in system design. A System boiler packages those components internally for a more self-contained installation. What electrical supply and cable size do I need? The 9kW model draws 41 A at 230 VAC. Your installer must provide a minimum 45 A MCB/RCB breaker and a minimum 6 mm² cable — though the actual cable specification should always be calculated against the specific installation conditions (cable length, route, ambient temperature). A linked isolator switch with a minimum 3 mm contact gap in every pole is also required. Because this is a new circuit, a Part P electrical installation certificate is legally required on completion. Does this boiler work with solar panels? Yes. The Strom Heat Only Boiler is compatible with solar PV divert systems. When paired with a solar immersion/divert controller, surplus generation from your panels can be directed to heat your home, reducing your electricity bill. It is also well suited to Economy 7 / Economy 10 tariffs for lower overnight running costs. Which thermostat or controls do I need? The boiler has no onboard programmer — external time and temperature controls are required by Building Regulations (Part L). You can use a separate programmer and room thermostat, or an all-in-one programmable room thermostat. The boiler's PCB accepts a standard switch-live signal, making it compatible with most third-party controls including smart thermostats. Strom also manufactures its own range of programmers and thermostats. How do I register the warranty? Register online at www.stromltd.com/guarantee within 45 days of purchase using the details on the registration card supplied with the boiler. Registration extends the warranty to 2 years (parts and labour in year 1, parts only in year 2). Only the legal owner of the building can register. Failing to register within the 45-day window reduces cover to 1 year. Can I install this boiler in a bathroom, cupboard or garage? The boiler can be sited almost anywhere provided the wall surface is non-combustible and rated above 100 °C, there is at least 100 mm clearance on all sides, and the location is not accessible to unauthorised persons. Where there is risk of access by children or unqualified individuals, it must be installed in a lockable enclosure. In areas prone to frost, ensure that an external frost stat is wired inline to supplement the built-in frost-protection mode.
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