Gas Water Heaters and Hard Water or Borehole Water

Water hardness – Hard water contains a higher than normal concentration of Calcium and Magnesium, along with various other minerals. Soft water has either had the minerals purified or neutralised from it. Excessive water hardness may change the taste of drinking water, cause soap and detergent not to bubble and clog or block plumbing systems or appliances. If you notice the bottom of your kettle or coffee machine is forming a white layer, then lime-scale build-up is an issue in your water system.

When heated, the chemistry of the minerals in borehole water changes and can separate, forming a build-up inside of plumbing pipes and appliances. This coating of minerals is called ‘scale’. The formation of ‘scale’ is more pronounced when the water is super-heated (as is the case with gas water heaters) causing the internal pipes of the heat exchanger to become clogged and blocked. If left untreated, the heat exchanger will malfunction or be permanently damaged.

Gas, solar and electric water heaters are severely affected by scale. Scale build-up prevents the efficient transfer of heat from the heat exchanger to the water – water will take longer to heat up and at a higher cost. The build-up of scale will also eventually lead to water temperature fluctuations and a reduction in the flow of hot water from the unit.

Paloma units heat water by passing cold water through a Copper Heat Exchanger. This heat exchanger is manufactured from very high-quality copper. Copper is used due to its properties of having a very high heat conductivity and physical strength. Due to the very high heat values (upward of 46kw) within the heat exchanger, hard water minerals will separate and stick to the interior of the copper pipes, eventually forming a blockage. If not rectified in time the heat exchange will eventually rupture.

Any unit installed on borehole water systems should undergo regular flushing – this is performed using vinegar, lime juice or a quality descaling liquid and pumping the solution through the Paloma for 20-30 minutes. The frequency of ‘flushing’ is dependent on the concentration of calcium in the water.

If not flushed regularly, noticeable signs of reduced water flow, reduced water temperature, or overheating errors (Error Code 14 or 15) will appear on the Paloma.

Options for dealing with hard water / groundwater

As each situation is different – water needs to be tested and water filtration/softeners built to specification. Yearly re-testing of water should take place due to the changeable nature of borehole water. Please check your manual for any specific water requirements. Regular flushing should always take place.

Water quality is VITAL to the longevity and efficient operation of your Paloma Gas Water Heater. Therefore to ensure the best and trouble-free performance the composition of water being used should not exceed the following parameters:

pH 6.5 to 8.5
TDS (Total Dissolved Solids) Up to 500 mg/L
Total Hardness Up to 200 mg/L (11.7 gpg)
Aluminium Up to 0.2 mg/L
Chlorides Up to 250 mg/L
Copper Up to 1.0 mg/L
Iron Up to 0.3 mg/L
Manganese Up to 0.05 mg/L
Zinc Up to 5 mg/L


Borehole water affected Paloma Gas Geyser
Borehole water affected Paloma Gas Geyser

Paloma Gas Water Heaters should be flushed every 3-6 months to try to help preserve the appliance and its unique parts. 

We would also recommend that you flush with vinegar to remove scale build-up.

You will need 5 litres of standard vinegar, a submersible water pump, a 20 litre bucket and washer / dryer hose set.

Click here to get instructions on how to flush your geyser

The use of Borehole Water does invalidate Paloma Gas Water Heater’s warranty however, regular care and maintenance will preserve the lifespan of the unit.


The use of Siliphos Crystals is a cost-effective method of reducing the formation of lime-scale. These crystals can be installed in a filtration system and usually last 3-6 months and can be renewed when necessary.

Please see more on our GWH warranty page


Paloma’s Gas Geysers must be installed in accordance with the below advice, to be covered by the Paloma warranty.

Our gas geysers are manufactured to suit the water conditions of most public reticulated water supplies. However, there are some known water chemistries that can have detrimental effects on the water heater and its operation and / or life expectancy. If you are unsure of your water chemistry, you may be able to obtain information from your local water supply authority. A Paloma gas geyser should only be connected to a water supply that complies with these guidelines, for the Paloma warranty to apply.

Change of water supply

The changing or alternating from one water supply to another can have a detrimental effect on the operation and / or life expectation of a heat exchanger in a continuous flow water heater.

Where there is a changeover from one water supply to another, e.g. a rainwater tank supply, bore water supply, desalinated water supply, public reticulated water supply or water brought in from another supply, then water chemistry information should be sought from the supplier or it should be tested to ensure the water supply meets the requirements, given in these guidelines for the Paloma warranty to apply.

Saturation Index 

The saturation index (SI) is used as a measure of the water’s corrosive or scaling properties. The saturation index figures stated are calculated using a water temperature of 80°C.

In a corrosive water supply, the water can attack copper parts and cause them to fail. Where the saturation index is less than –1.0, the water is very corrosive and the Paloma warranty does not apply to a copper heat exchanger in a continuous flow water heater.

In a scaling water supply, calcium carbonate is deposited out of the water onto any hot metallic surface. Where the saturation index exceeds +0.80, the Paloma warranty does not apply to a copper heat exchanger in a continuous flow water heater.

Water that is scaling may be treated with a water softening device to reduce the saturation index of the water.

Saturation Index of Gas Continuous Flow Geysers