What scale does
Scale forms on the hottest surfaces: the element of an electric heater, the heat exchanger of a gas heater or combi boiler, and the coil in a cylinder. Even a thin layer acts as insulation, so more energy is needed to heat the same water, and the element or exchanger runs hotter than it should.
Loose scale also collects at the bottom of storage tanks, reducing their useful volume. In instant heaters and combi boilers it narrows the small passages until flow drops and the water turns lukewarm.
Signs your heater is scaling up
Hot water that runs out sooner than it used to, a heater that takes longer to warm up, rumbling or crackling noises as it heats, white flakes in taps and showerheads, and lower flow from the hot side are all typical. A boiler that “kettles” with a loud boiling sound is usually scaled inside.
Turning the temperature down is not the answer. It slows scale a little but brings the water into the range where Legionella grows. The fix is to treat the water and service the heater.
Treatments that work
A water softener (ion exchange) removes the minerals that cause scale and protects the whole house, at the cost of space, salt and periodic regeneration. Polyphosphate dosing units are smaller: they keep minerals in solution so they do not stick, and need a refill now and then. A sediment filter before the heater keeps sand and rust out. Magnetic and electronic conditioners are widely sold, but the evidence for them is mixed.
Central heating is different. The heating side of a boiler system is a sealed loop filled once, so it brings in no new minerals. Filling it with treated water and an inhibitor, and fitting a magnetic filter, keeps the boiler and radiators clean for years.
Servicing: descaling and the anode
Storage heaters and cylinders should be drained and flushed, the element descaled or replaced, and the magnesium anode checked at service. The anode corrodes on purpose to protect the tank; once it is used up, the tank itself starts to rust. Instant heaters and combi boilers can have their heat exchangers chemically descaled.
Solar water heaters suffer too, especially direct systems where tap water runs through the collectors. In hard-water areas an indirect solar system, with a sealed loop through the collectors, avoids scale inside the panels altogether.
Protect your heaters before scale costs you
If your hot water has slowed down, run out sooner or started to rumble, the heater most likely needs descaling, and the water probably needs treating so it does not happen again. How hard your water is, and how much hot water you use, decide which treatment is worth it.
Conversion EG has installed and maintained hot water and heating systems in Egypt since 2010, with one team from design and supply through installation and maintenance. Book a visit and we will service your heaters and recommend the right protection for your water.
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