Scale in water heating systems

Most people are familiar with the build up of scale on the elements of kettles and immersion heaters in hard water areas in the country, however, scale formation in closed circuit water heating systems is rarely considered.

In central heating systems, scaling is caused by the deposition of either lime or black iron oxide corrosion debris. Lime scale consists of calcium carbonate (calcite) with lesser amounts of other calcium salts such as the sulphate. Sometimes lime scale deposits contain corrosion debris which has become trapped.

Most people are familiar with the build up of scale on the elements of kettles and immersion heaters in hard water areas in the country, however, scale formation in closed circuit water heating systems is rarely considered.

In central heating systems, scaling is caused by the deposition of either lime or black iron oxide corrosion debris. Lime scale consists of calcium carbonate (calcite) with lesser amounts of other calcium salts such as the sulphate. Sometimes lime scale deposits contain corrosion debris which has become trapped.

Unlike most substances, most calcium salts become less soluble as the temperature rises (inverse solubility). Such salts are naturally present to some degree in all mains water supplies, therefore, any system where mains water is heated is liable to suffer from lime scale formation.

The formation of scale in a central heating system has three important effects:

• Causes kettling noise
• Reduced efficiency
• Increases thermal stress in metal

My central heating boiler (Potterton Netaheat Electronics 16/22) was installed about 15 years ago. I understand that we have a close system. The boiler is cast-iron made and we have a hot water cylinder to store the hot water.

During the last few months, the boiler made a lot of noises and does not heat enough water for our use. When we switch on the hot water from the programmer, the boiler comes on for a short while only. Last week, we called out BG. The engineer replaced an electronic part and he told us that there are too much air in the system causing the noises. Still, we did not get much hot water. On Monday, another two BG engineers came again. They said part of the our pipe works could be block up and we should that part replaced.

On Tuesday, we have no water (hot or cold) at all from the bathroom taps. We also have no water in the toilet. I checked the cold water storage tank and it was nearly empty. I eased the ball-valve a bit and water started to flow into the tank. When the tank is nearly full, we still did not get any water in the bathroom. I called out a plumber. He said we had air-lock in the system and got rid of the air for us. He advised us to use an inhibitor to get rid of the noise and to clear the system. I want to find out if I could use Fernox products to cleanse the system without having to pay a lot of money to have the pipe work replaced.

Thanking you in advance.

Regards Paul Lee

The cheapest method to cleaning the boiler and system to prevent a reoccurrence of the noise problem is using the Fernox Heavy duty Restorer and Fernox DS-40 boiler descaler as outlined by Fernox, so preventing boiler replacement and re-plumbing.

Firstly drain and flush the entire heating system with plain water until non-foaming. Circulate a 2% solution (2 Litres per ten radiators) of Fernox Heavy Duty Restorer in the whole central heating system either continuously for 48 hours or intermittently under normal load conditions for a week i.e. 7 days on a 6 hour heating cycle. Drain and flush the whole system until water is clear and to ensure flocculated sludge and cleaner are removed from the system. At least three complete changes of water are likely to be required. Were pipe-work is present below the drain-off points, I would recommend operating the pump for 10minutes between each flush, so ensuring any material remaining in the low points is diluted further. Secondly, to clean any baked on debris I would also do a separate boiler descale by isolating flow and return pipes to the heating circuit, or by closing the lock shield and wheel head valves to all radiators except one. Use a 2% solution (for typical domestic system, a restricted circuit on 2% DS-40, will require only half a 2Kg container) of Fernox DS-40. Allow this to circulate for 24 hours at 700C. Drain the system whilst still hot and flush with plain water.

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After cleaning, treat the system with a 4% solution of Fernox MB-1 which will render the water non-corrosive to steel, copper, aluminium and brass, prevent any scaling by fuel wasting water hardness salts so helping to minimise the occurrence of boiler noise. I hope this information helps. If you need any further help or advice, Fernox Technical Help Line is an excellent source of information on 01799 521133.

Adrian

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Many thanks for your advise and the very detailed instructions. Last Saturday, I drained and flushed the whole system with plain water. It took six flushes to clear all the sludge. I then put Fernox Heavy Duty Restorer into the expansion tank after the refill. When I switched on the central heating, all the noises had gone.

I then switched on the hot water. At first there were some noises but these noises quickly disappeared. Next to my hot-water cylinder was a 1" header-pipe. It has an ½" branch-off. This branch-off was suspected blocked. After switching on the heating for an hour, this branch-off was cold while the header-pipe very hot. Gradually, the branch-off started to get hot from the joint and then the whole pipe became hot.

I believed that the Fernox Heavy Duty Restorer had unblocked the branch-off. I will let Fernox Heavy Duty Restorer carry on cleansing the system for two weeks. I will then follow the rest of your instructions. Once again, thank you very much. Regards Paul

Lee

Now that you have spend the time and effort in de-scaling your boiler with Fernox Heavy Duty Restorer, may I suggest that you consider fitting the Hydroflow HS38 physical water conditioner to stop the lime scale forming again.

The technology used is not the same as any other water conditioner available, all the others on the market have to have water to flow, which means no flow no conditioning, and as we all know water doesn't flow 24 hours a day in domestic situations. The Hydroflow unit uses a patented method of transmitting a signal directly into the water, this treats the complete system all of the time. Therefore, the water it is already conditioned at the point where it is being heated on demand.

A suitable model for your Potterton would be the model HS38, the most competitive pricing is currently from www.plumbworld.co.uk, you can also find further information about the technology on www.hydroflow.com . There is a 3 year no quibble money back guarantee, if the unit doesn't work you can get your money back I hope this is of further interest to you, and know it will save hours of dismantling and cleaning in the future

Regards

Glyn