Limescale is the nuisance of the hot water and humidifier systems, causing interruption to supply by damaging key system components such as immersion elements. Limescale can also narrow the inside of hot water pipes, restricting the follow of water and eventually blocking them with the build-up of a white chalky deposit.

Early signs of limescale damage can be, poor heat transfer, i.e. hot water not achieving desired temperature or taking too long to reach temperature.


Limescale is a naturally forming white chalky substance in heated water, caused by naturally occurring minerals in the ground, such as, calcium and magnesium.

Limescale acts a blanket over a heat source, impeding its ability to operate and requiring more energy to optimally function.

Hard water – the cause of limescale

Limescale builds up when water containing these minerals is heated, leaving a white chalky deposit on heating components such as kettles, taps, shower heads and immersion elements within hot water systems. The water containing these minerals is known as hard water. Hard water is completely safe to consume. It often tastes nicer to drink than soft water, due to its higher mineral content. However, when heated it fixes itself to surfaces in the form of a chalky deposit.

Limescale damage

This video shows where the building facility manager noticed an extended hot water regeneration time and alerted the service engineer. Upon investigation a corroded immersion element was discovered, having been attacked by a build-up of limescale.

While this video displays more severe limescale damage in a humidifier in an air handling unit. The scale of this damage is an example to what can happen with untreated hard water over an eight-month period.

Heating system – hot water source

Hot water generation is an essential function of the heating system. The heating system is not only a source of heat, but it also provides hot water throughout a building, to taps, showers and appliances.

Therefore, any damage to this system especially in a commercial building where demand for reliable hot water is essential to a business-critical process, can cause downtime for repairs. In turn this could not only cost the business in system repair work, but also in terms of their reputation amongst staff, customers and the public alike.

Remove limescale from hot water system

A chemical de-scaler can be used to remove limescale and other deposits from a hot water system by power flushing the system. This is a reactionary measure. It doesn’t nullify the source of the damage, nor will it repair damage to system components, such as the corroded immersion element in the first video above.

There are more sustainable, preventative measures that can be utilised. However, it is recommended that you use a water testing kit first, to confirm hard water is present. There is no point in treating or putting preventative measures in place if your water isn’t hard.

Check if you are living in a hard water area on Irish Water’s website

Preventative measures for a building facility manager

1. Install a water softener

Installing a water softener to the incoming mains water supply can effectively convert hard water to soft.
The mains water passes through a standalone water softener tank, stripping away the minerals that cause hardness in the water.

2. Install a sacrificial anode

The purpose of the sacrificial anode is to attract limescale deposits and sacrifice itself, preserving the immersion element and other parts of the hot water system from corrosion.

The sacrificial anode is a metal rod that is inserted into a water heater or hot water calorifier.

A warning light on a gas-fired calorifier will inform you on when the sacrificial anode has to be replaced. Other systems require a drain down and inspection of the anode to confirm its worthiness.

Thermodial’s approach

Thermodial’s approach is to set up a planned preventative maintenance (PPM) regime. This approach is the most risk averse, energy efficient and cost-effective measure.

Installing a water softener and a sacrificial anode are preventative measures. Like any other parts of your heating, ventilation, air conditioning (HVAC) system, these installations require regular maintenance service tests and checks to confirm their correct and efficient operation.

The implications of not having such a regime in place are evident from the two videos. Downtime to hot water systems because of time-consuming drain-downs or repairs to internal parts mean that a PPM regime will pay for itself many times over.

Explore our full PPM capabilities.