Water hardness
Wherever you are in the country you can gauge the problem of limescale formation
by taking a look in a year-old kettle. Officially, the worst location for limescale
is Hartlepool. Nationally, Kent, East Anglia and here in the Thames Valley are the
worst areas. We have considerable ‘chalk’ deposits to the north and south of the
Thames River. Hence our drinking water has a high content of calcium. Hard water
is formed when rainwater dissolves calcium and magnesium salts as it finds its way
down through limestone or similar rock. Heating causes the dissolved calcium and
magnesium bicarbonates to break down to form a solid carbonate (limescale). This
is harmless to health but causes deposits in hot water systems and kettles. Water
from rock formations, such as granite, which contain little calcium and magnesium,
is naturally soft.
The hardness of water is measured as milligrams per litre of calcium carbonate, i.e.
200mg CaCO/litre. Milligrams per litre is the same as parts per million (ppm). You
may also see hardness expressed as milligrams of calcium per litre - these can be
converted into mg CaCO/litre by multiplying the reading by 2.5. As a general indication
the soap and detergents industry classify water as follows:
Hard water contains more than 200 mg of calcium carbonate per litre
Moderately hard water contains 100 to 200 mg of calcium carbonate per litre
Soft water contains less than 100 mg of calcium carbonate per litre
Water in Reading is around 300 CaCO/litre (or 300 parts per million (ppm) - or 22
degrees Clark) and is classed as Very Hard.
Much has been made about electronic so-called ‘water softeners’ in our trade press
and newspaper articles and advertisements. Let us though be clear about these: they
are not softeners in the traditional sense since they do not soften the water. If
they indeed ‘work’ in every situation then we have yet to witness it. It would appear
that flow, pressure and amount of use have a considerable impact on their effectiveness.
It should be remembered that we descale heat exchangers every working day, and the
vast majority of the boilers we see already have a scale inhibitor fitted. One particular
electronic scale inhibitor changes the molecular structure of the limescale so that
it becomes ‘sandy’. It therefore collects in the first elbow joint on the hot water
system. Two of the inhibitors available that use polyphosphate dosing should, in
our opinion, be taken off the market, as their action can be worse than having nothing
at all! The polyphosphate (a white, powdery substance) breaks off and clogs the water
inlet pipes of combination boilers. The ONLY thing we recommend is our own LimeStop.
Quite simply, it works - we guarantee that.
Limescale formation is very damaging, not just an inconvenience. Deposits on the
inside wall of a heat exchanger will take hold rapidly once the initial layer has
been laid down - due to its molecular structure. Its effects will be considerable
fuel wastage (due to the fact that the limescale itself has to be heated), reduced
water flow and even overheating. The latter can cause damage to the boiler. Limescale
deposits of just one-sixteenth of an inch can cause a loss of efficiency of 10%.
To add to this the water flow will be reduced. Indeed, a 5% reduction in diameter
will cause a 23% flow drop. If you removed all the scale from the water a family
of four uses in a year it would weigh 70kg - about the weight of an adult.
Our service: We employ a solution of acid and water. This is highly effective and
can remove the deposits in a heavily-scaled combination boiler in under two hours.
For mains-fed cylinders such as IMI, Powermax and Gledhill, the amount of solution
used will be many times this, but would be a varied dose according to the severity
of the limescale deposits. Our acids are not jellified and wash out immediately after
the de-scaling process. Indeed, we have carried out a 2-year descaling operation
of drinking-water supply pipes (in Berkshire and Hampshire) for Thames Water. A simple
pH test shows no signs of residue acid.
I always descale the hot water pipe network - not just the boiler’s heat exchanger.
This is important. Far too many engineers - rather than descale - simply replace
the heat exchanger. But this does nothing for the limescale that is present within
the outlet pipes!
Waters heaters (and some combination boilers) tend to raise incoming temperature
by 35 degrees C. So if the water coming into the boiler is 10 degrees then the overall
temperature of the water at the taps will be 45 degrees. If it were coming in at
15 degrees then the temperature would be 50 degrees at the taps. Limescale forms
rapidly after 60 degrees. Many modern boilers adjust the temperature to ensure that
it is always the same, no matter what the time of year (and therefore the incoming
temperature). The figure of 35 degrees is usually based on a flow rate of 9 litres
per minute. Obviously, if you increase the flow, then the temperature drops. If you
decrease the flow then the temperature increases. This is why limescale formation
can be cyclical. It will build up and reduce the flow. That decrease in flow raises
the temperature of the water. The hotter water results in more limescale formation.
