Baxi Amptec S4 4kW Electric System Boiler
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The Baxi Amptec S4 is a 4 kW electric system boiler for wet central heating — now sold under the Baxi brand, previously Heatrae Sadia. It needs no gas supply and no flue, runs both radiators and underfloor heating, and carries its circulation pump, expansion vessel and HMI display inside one compact, UK-built unit that fits a 290 mm deep cupboard.
Applications & suitability
Sealed wet central heating in homes without a gas supply. Runs radiators or underfloor circuits from 30–80 °C, and with pump, expansion vessel and controls built in it drops into a 290 mm deep cupboard with no flue to route.
A new electric heating installation or a like-for-like electric boiler refurbishment — flats, off-grid properties, social housing and landlord upgrades. Baxi state it can also be used in conjunction with a solar PV battery.
Certified OpenTherm, so it pairs with OpenTherm controls including the Baxi uSense 2 for best efficiency. As a system boiler it works with a separate hot water cylinder, and it joins Baxi’s existing Amptec and Electromax electric range.
Not a combi — stored hot water needs a separate cylinder. At 4 kW this is the smallest model in the range and suits low heat-loss properties; for larger demands step up through the S6–S18. Three-phase properties should look at the S14 or S18.
Key specifications
| General | |
| Brand | Baxi |
| Model | Amptec S4 |
| Boiler type | Electric system boiler |
| Output (central heating) | 4 kW |
| Power supply | Single phase |
| Performance | |
| Flow temperature (max) | 80 °C (adjustable from 30 °C) |
| Modulation ratio | Up to 9:1 |
| Controls compatibility | Certified OpenTherm (incl. Baxi uSense 2) |
| Dimensions & weight | |
| Packaged dimensions (H × W × D) | 889 × 444 × 350 mm |
| Lift weight (dry) | 20 kg |
| Installed weight (filled) | 21 kg |
| Packaged weight | 23.2 kg |
| Warranty & provenance | |
| Warranty | 2 years |
| Country of manufacture | United Kingdom |
Installation & compatibility
No gas and no flue, so no Gas Safe engineer is needed. The fixed electrical connection must be made by a qualified electrician — in England and Wales this work falls under Part P of the Building Regulations. A filling loop and rear pipework kit are available separately.
Related & next steps
For filling and pressurising the sealed system at install.
View filling loopRoutes pipework behind the boiler for a tidier first fix.
View pipework kitAlso available in 6 kW, 8 kW, 12 kW, and three-phase 14 kW and 18 kW models.
Ideal For
Low heat-loss flats and smaller homes off the gas grid that need a compact, flueless system boiler for radiators or underfloor heating — with next-day national delivery or click & collect from our Reading trade counter.
