Physical, electromagnetic water conditioners do not provide sufficient protection. We’ve seen the evidence of this with organisations which have cut gas from their systems, transitioning to all-electric hot water with DHW buffers heated by immersions. Despite market-leading physical conditioners installed on both the cold inlet and secondary return, every site in hard water reported failures of immersions within four months to a year. Only a salt-based water softener will offer adequate protection, but there is a better, and more cost-effective way of addressing limescale, and that is to use an electric boiler instead.

By employing an indirect method of water heating and controlling temperatures the all too common problem of destructive limescale build-up can be effectively eliminated. Working in conjunction with an indirect cylinder to provide DHW in an effectively sealed ‘primary loop’, the expectation is for little to no scale build as the boiler recirculates the same finite amount of water through the heat exchanger. Key to this is maintaining a relatively low (80°C) temperature reducing heating intensity on surfaces that would otherwise accelerate scale formation. The use of an electric boiler supersedes an immersion because it comes complete with a range of controls which would otherwise need to be addressed via the building management system (BMS), which would require costly switchgear and an expert electrical contractor or BMS specialist.

Controls offer a variety of options, including soft start, soft stop; load sharing among internal heating elements, stepped modulation down to 33% of load; control of maximum flow temperature; control of kW output (downrating); overcurrent and overheat protection; weather compensation; plus, fault relay for alarm output to BMS. All of this helps to monitor and maintain the necessary consistency of water temperature and avoid points of high-intensity temperature.

Although an electric boiler will use a few extra Watts for a small pump, it will offer a heating efficiency identical to immersion heaters. However, as scale formation increases immersions will take longer to heat water meaning the boiler will offer greater efficiency over time. Also, as the electric boiler efficiency is not dependent on flow temperature, it can still provide high primary temperatures that give short cylinder reheat times and easily achieve the required temperatures for regular legionella purging. It is worth noting that the presence of limescale also provides a surface that can help promote legionella growth within the calorifier.

You could argue that immersions are easier, cheaper options, that is certainly true if you are installing a 12 kW immersion into a large tank, which will cost you £300 to £700 and, if well maintained, should last. However, if you are trying to add, for example, a 24 kW immersion to a smaller tank, then the complexity of that unit will see the pricing rise quickly to as much as £1500, plus the cylinder will require larger access which also comes at an additional cost. That is also what you would also expect to pay for a 24 kW electric boiler, with all the advantages it brings.

With little to no scale build-up, an electric boiler system will exhibit increased reliability and improved response time, whereas immersions will take longer to heat water as scale formation increases around the element hampering its efficiency. The use of multiple heating elements within the boiler also avoids the single point of failure issue seen with immersions, providing built-in redundancy, and when balanced by controls for most efficient use will see system lifespan improve.

With less need for descaling maintenance costs are reduced. Servicing is also easier as the boiler can be wall or cylinder-mounted on either side allowing for flexible installation clearance without the need to withdraw a long immersion heater. There is also no need to drain down the cylinder, which would otherwise interrupt water provision during maintenance or repair.

Compared to direct electric immersions, electric boilers offer an EcoDesign-compliant, cost equivalent, simpler to control, ultimately more efficient to run, and easier to maintain system that has a greater lifespan. It should be the technology of choice for any organisation seeking to secure low-carbon DHW in hard water areas.

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