A gas-engineer’s brand makes a serious electric play.
For installers, Baxi has long been one of those names that just sits comfortably on a quote. A heritage stretching back to 1866, manufacturing held in Preston, parts that turn up the next day, and a customer support line that picks up. Front-access serviceability, sensible mounting templates, predictable flueing — the Baxi 400, 600 and 800 ranges earned their place in vans across the UK because they are boring to install in the best possible way. No surprises on the wall, no surprises in the warranty department.
The Baxi Amptec S electric system boiler is the brand’s attempt to bring that same installer-first DNA to a property without a gas main. It is not a hedge or a token electric SKU. It is a UK-manufactured, six-model range with proper modulation, OpenTherm compatibility, an integrated pump and expansion vessel, and a cabinet shallow enough to drop into a 290 mm cupboard. In other words: an electric boiler that behaves on site like a gas one.
— Rob Pearse, Residential Business Director, Baxi
This post is written for installers specifying or fitting an electric system boiler in a UK home off the gas grid — new builds, high-rise dwellings, flueing-restricted properties, or retrofit jobs where the existing gas appliance is being decommissioned. Below you will find the Amptec S in context, the six output sizes mapped to dwelling type, the indirect cylinder pairings we stock, recommended system protection, and a quick guide to the AmbiZen control range it pairs with.
Where the Amptec S earns its place on the spec sheet
Electric system boilers occupy a specific corner of the UK heating market — properties without mains gas, where a heat pump is not viable (no external wall, conservation area, listed building, top-floor flat, restricted budget), and where a traditional G3-qualified install is wanted alongside a stored hot water cylinder. The Amptec S is engineered for exactly that brief.
Built-in hydraulics
Circulation pump and expansion vessel are integrated. Pipework lives inside the casing, cutting install time and pipework on the wall.
9:1 modulation
Duty cycling of heating elements matches output to demand — a step change versus older on/off Amptec models. Cuts running cost and short-cycling wear.
OpenTherm-ready
Pairs natively with OpenTherm controls including Baxi uSense 2 and the new AmbiZen range. Weather-comp and load-comp behaviour straight out of the box.
Solar PV compatible
Designed to pair with PV and PV battery systems — an attractive route for social housing providers and homeowners chasing self-consumption.
Single-phase and three-phase
Six models cover both incomers. The 4, 6, 9 kW units sit comfortably on a domestic single-phase supply; larger outputs are available where three-phase is in.
Compact and serviceable
290 mm cabinet depth fits an airing cupboard. The HMI display aids commissioning, fault finding and end-user explanation on handover.
At a glance — what Baxi has packed into the Amptec S
A UK-manufactured electric system boiler designed around the realities of a domestic retrofit or new-build install. No flue, no condensate run, no gas connection — just an electrical supply, the heating circuit, and a feed to an indirect cylinder.
Sizing the Amptec S against the dwelling
Six output sizes give meaningful granularity. As a starting frame, the table below maps Amptec S outputs to typical UK dwelling profiles — always validate against a full heat-loss calculation and the cylinder reheat demand, particularly where wet underfloor heating or larger Megaflo capacities are in play.
| Output | Supply | Typical dwelling | Indicative cylinder |
|---|---|---|---|
| 4 kW | Single-phase | Studio / 1-bed flat | 70–125 L indirect |
| 6 kW | Single-phase | 1–2 bed flat, small terrace | 125–145 L indirect |
| 9 kW | Single-phase | 2–3 bed terrace / semi | 170–210 L indirect |
| 11 kW | Single-phase | 3 bed semi / small detached | 210–250 L indirect |
| 14 kW | Three-phase | 4 bed detached | 250–300 L indirect |
| 18 kW | Three-phase | Larger detached / light commercial | 300–400 L indirect |
Installer note: Always confirm the property’s incoming supply, main fuse rating and meter tail capacity before sizing — particularly above 11 kW. Three-phase outputs require a notification to the DNO under G99 only if paired with grid-export-capable PV; the boiler load itself is straight consumption.
The product
Baxi Amptec S Electric System Boiler — 4 kW to 18 kW
A compact, modulating electric system boiler built in the UK by Baxi. Six outputs from 4 kW to 18 kW, single-phase and three-phase, OpenTherm-ready, with integrated pump and expansion vessel inside a 290 mm cabinet. Pairs with any indirect unvented cylinder for hot water, and works with both radiators and wet underfloor heating. Backed by a 2-year parts and labour warranty.
From £1,190.00 inc. VAT
Pairing the Amptec S with the right indirect cylinder
Because the Amptec S is a system boiler, it relies on an indirect unvented cylinder for stored hot water. Get the cylinder right and the install is straightforward; get it wrong and the homeowner ends up complaining about reheat times. We stock the cylinder ranges most often paired with Baxi system installs in the UK — below are the four routes worth considering, plus a heat-pump-ready horizontal option for retrofit jobs where loft space is the only home for the cylinder.
Heatrae Sadia
Megaflo Eco SystemReady Indirect
Factory pre-plumbed and pre-wired for direct connection to a system boiler — the fastest cylinder swap on the market. Sizes from 170 to 300 L. The first choice when site time is tight or the job is being signed off in a day.
From £1,900.00 inc. VAT
Heatrae Sadia
Megaflo Eco Indirect
The UK’s market-leading indirect unvented cylinder. Sizes from 70 to 300 L, duplex stainless steel, with a 3 kW backup immersion. The standard pairing for the 4–11 kW Amptec S in a domestic install.
From £1,200.00 inc. VAT
Heatrae Sadia
Megaflo Eco Plus Indirect
High-capacity sister to the standard Megaflo Eco. Sizes from 250 to 570 L, engineered for large detached properties and light commercial. The right cylinder to pair with the 14 kW and 18 kW Amptec S where demand is genuine.
From £2,335.00 inc. VAT
Joule
Cyclone Plus Indirect Horizontal
Horizontal duplex stainless steel cylinder for loft or low-headroom installs. Sizes from 120 to 300 L with a fast-recovery coil and 25-year warranty — the sensible answer where there is no airing cupboard.
From £895.00 inc. VAT
Telford
Tempest Indirect Horizontal Heat Pump Cylinder
Horizontal stainless steel cylinder with a heat-pump-grade coil — a useful long-term-thinking spec where the property may upgrade to an air source heat pump down the line. Pairs well with the Amptec S today and keeps the cylinder in place for the next system change.
From £1,120.00 inc. VAT
System protection — the non-negotiable bit
An electric boiler is more sensitive to sludge and magnetite than a gas appliance. The heating elements live directly in the heating circuit; debris that would slowly cook on a heat exchanger will, on an Amptec S, settle straight onto the elements. A magnetic filter is therefore not an upsell — it is an essential part of a clean install and, for many warranty claims, the difference between cover and an out-of-warranty repair.
ADEY
MagnaClean Professional 2 Filter (22 mm)
The UK’s first-choice magnetic filter, sized 22 mm to match standard domestic heating pipework. Bi-directional flow, 550 ml fluid capacity, EPDM seals throughout, and a stainless-steel magnet housing. Fits in 50 mm of clearance top and bottom, services in under two minutes, and is the protection you will want documented on the commissioning report for any Amptec S install.
£99.00 inc. VAT
Smart control — pair with Baxi AmbiZen
The Amptec S talks OpenTherm. The control range built specifically to take advantage of that is Baxi’s new AmbiZen family, launched in May 2026. Single-channel for a one-zone install, or extend the same gateway into a multi-zone system by adding additional thermostats — useful where the property has a clearly defined sleeping zone and living zone, or where wet UFH and radiator zones are running in parallel.
Baxi
AmbiZen Smart Thermostat (Single Channel)
Wireless smart thermostat that pairs with a dedicated AmbiZen Gateway. Controls the boiler at the wall, in the app, or by voice. The recommended primary control for any Amptec S install.
£157.00 inc. VAT
Baxi
AmbiZen Additional Thermostat — Multi-Zone
MPN 7907002. Drops onto the existing AmbiZen gateway already wired to the boiler and gives a second zone its own independent wireless room thermostat. Add one per additional zone.
£63.00 inc. VAT
Spec tip for installers: When quoting the Amptec S, lead with the AmbiZen single channel as the default control and price additional thermostats as line items only where the property genuinely has separate zones. Avoid quoting a third-party OpenTherm stat — AmbiZen is the cleanest pairing on the manufacturer’s commissioning paperwork and the path of least resistance through Baxi support if a fault is reported.
Installation considerations worth flagging on the quote
Electrical supply check
Verify the incoming main fuse rating, meter tails and consumer unit capacity before quoting the kW size. Above 12 kW, a three-phase supply is typically required and a DNO conversation may be needed.
Cylinder coil sizing
Match the cylinder coil rating to the boiler output. A 9 kW Amptec S into a fast-coil 210 L Megaflo is a balanced pairing; underpowering the boiler against a large cylinder makes reheat times the customer will notice.
G3 unvented certification
As with any unvented cylinder install, the engineer fitting must hold G3 certification. The boiler itself does not need Gas Safe registration — this is the single biggest operational difference versus a gas system boiler swap.
System flush & filter
Power-flush the existing heating circuit on a retrofit, dose with inhibitor and fit a magnetic filter at commissioning. Document it on the certificate — this is what protects the 2-year warranty.
Installer FAQ
Does the Amptec S need a flue?
No. The Amptec S is an electric boiler — no combustion, no flue gases, no condensate. The only services it needs are an electrical supply, the heating circuit flow and return, and a connection to an indirect cylinder for hot water. This is what allows the 290 mm cabinet depth and the flexibility on siting.
Can the Amptec S run wet underfloor heating directly?
Yes. The 30 °C to 80 °C flow range covers both standard radiator circuits (typically 55–65 °C) and wet UFH (typically 35–45 °C). Where a property mixes radiators and UFH, use a blending valve and zone control or run separate zones via an AmbiZen multi-zone setup.
What controls is the Amptec S compatible with?
The Amptec S is OpenTherm compatible. It pairs natively with Baxi’s own AmbiZen smart thermostat range and uSense 2 control. Any third-party OpenTherm-certified stat will also work, but the cleanest paperwork trail and warranty support comes from staying within the Baxi control family.
Does it qualify for the Boiler Upgrade Scheme?
No. The Boiler Upgrade Scheme is for air source and ground source heat pumps and biomass — electric boilers are not eligible. Where a customer is set on electric heating but a heat pump is not feasible, the Amptec S is a sensible specification but it is not grant-supported.
What is the warranty?
The Amptec S carries a 2-year parts and labour warranty as standard. As with any Baxi product, the warranty depends on competent installation, a documented commissioning record, and annual servicing. Fitting a magnetic system filter at install is recommended for warranty support. Warranty registration via www.baxiworks.co.uk.
A 159-year UK heritage brand making its electric statement
Baxi was founded in 1866. Today it manufactures in Preston, is part of BDR Thermea Group, and is consistently rated “Excellent” by tens of thousands of UK customers on Trustpilot. The Amptec S is the brand bringing that reputation to bear on the electric system boiler category.
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