Most central heating systems contain some magnetite sludge, many old systems contain excessive amounts. If you install a new boiler in a system containing excessive amounts of sludge it can be disturbed around the system and into your brand new boiler.
Magnetite sludge is the principle cause of system replacement. It is present in the majority of heating systems as a thin, black liquid. However, it is often thick and oily. At this stage it is highly damaging to a system's performance and will ultimately cause system failure if left unchecked.
What Is Magnetite Sludge?
Although your radiators are probably nicely painted in a glossy white, the fact is that on the inside they are bare steel. Similarly, if you have an old-type boiler it’s highly likely to have a heat exchanger made of cast iron. The majority of systems suffer from bubbles of air. When air gets in, corrosion will take place. The boiler’s heat exchanger and the radiators will quite simply start to rust from the inside. This is what Magnetite Sludge is, primarily. Examined closely it often looks like the iron filings that you used to sprinkle over a magnet in sciences lessons at primary school. There may even be large particles of iron and steel.
Why Is The Water Black?
If you take a sample of water into a jar then it will be dark grey in colour or even black. However, let that water settle for a few minutes and the magnetite sludge will fall to the bottom. The water will clear and the sludge will lie in the bottom of the jar as a thick, oily-looking substance. Of course, this will settle into the bottom of your system too. This is why sludge often affects the downstairs circuit first in a two-storey home.
Is This Damaging?
Very! The fine magnetite will enter all the valves on the system. It will cause radiator valves to stick, or fail to close. It will ‘gum-up’ thermostatic radiator valves and render them useless. It will coat the inside of the Diverter valve (the valve that decides whether your system water goes to heating or hot water) in a gooey mess that will stop it working correctly. It will also attack your circulating pump - eventually causing its failure. Unfortunately, this is often ignored by plumbers. The pump is usually the first to succumb to the effects of sludge and come to a grinding halt. However, often the homeowner calls in a plumber who simply replaces the pump, but says little or nothing about the cause. It should be an alarm call as to what’s going on in the system and he should inform you that your system needs the MagVent
The Boiler Is Noisy
Well it would be! All that sludge will get baked-on over the years onto the walls of the heat exchanger. It will build up, and slow the water from leaving the boiler. The boiler will therefore overheat - and thus become noisy. Both limescale and sludge are good insulators of heat, so it will also cost you much more in fuel. That sludge has to be heated too.
Could I Have Limescale As Well?
Possible, but unlikely. Limescale forms in hard water areas only - obviously. Systems will get an initial ‘dump’ of calcium on first fill of water. However, the average system would get about thirty grams. Pretty much nothing really, although even that can cause a boiler to ‘wheeze’ as it’s usually concentrated at the boiler itself. Your system heats the water and sends it out to the radiators. That water comes back and is re-heated. It’s the same water. We get limescale in kettles because the water is obviously constantly changing, but system water is the same water - just re-heated, so there shouldn’t be any fresh water with fresh calcium. BUT, if a system leaks water (or a sealed system is very often re-pressurized) then this IS fresh water. Limescale will form - and form rapidly. Don’t worry too much about removing radiators to decorate. As long as you don’t redecorate every room every few months then it should be okay.
What Causes Air To Get Into The System?
Air can get in when water gets out. Leaks of water from joints or even pin holes in radiators will cause air to get into the system. But there are other factors. ‘Open’ systems (the type with a small tank - usually in the loft) will have a pipe called an Open Vent looped over into the water tank. This pipe must extend for some distance before looping over the tank. If it doesn’t then it can dribble water out when the system gets warm. This will oxygenate the system water (the water actually sucks air in) in much the same way as a garden pond is oxygenated by a fountain or water fall. On a pond, it’s a good thing; on a heating system it’s disastrous! Water simply laying in the tank will also absorb oxygen - it gets saturated with oxygen. If a system has not been designed or installed correctly then the Open Vent pipe can actually eject water into the tank when the pump is running (‘pumping-over’). This can cause a brand new system to ‘sludge-up’ in a matter of months! However, it’s cyclical. Sludge can actually cause the system to ‘pump over’ in this way also.
What Else Can Cause Sludge?
When a system is first installed there are naturally some chemicals present. If the system is in soldered copper joints then there can be soldering flux. This MUST be flushed out when the system is first filled with water. Not only that, but the system must be adequately flushed using a light cleansing chemical. All too often this is not the case at all. These chemicals will react and actually cause corrosion to start. Similarly, if a system is power flushed with an acid then great care must be taken to ensure it is adequately flushed from the system - otherwise it can actually cause sludge to return faster than before! This is because residues of acid will add to the corrosion process. |
