jetflo

Although your radiators are probably nicely painted in a glossy white, the fact is that on the inside they are bare steel. When air gets in, corrosion will take place. The boiler’s heat exchanger and the radiators will quite simply start to rust. This is what ‘sludge’ is, primarily.

IS THIS DAMAGING?

Very! The fine magnetite will enter all the valves on the system. It will cause radiator valves to stick, and cause thermostatic valves to stay open. It will ‘gum-up’ thermostatic radiator valves and render them useless, coat the inside of valves and sensors in a gooey mess that will stop them working correctly, and 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 sludge and come to a grinding halt. However, the homeowner calls in a plumber - who 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.

THE BOILER IS NOISY

All that sludge will get baked-on over the years onto the inside 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?

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. Your boiler 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.

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 air. 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.

Power-flushing

I’ve lost count of the number of plumber’s websites that I’ve read about power-flushing - which wrongly explain what could be happening and graphically show that they don’t even understand what ‘sludge’ is! It’s rather sad, and also a little disturbing, in that they are let loose on client’s heating systems with a misunderstanding of the problem, and how to put it right. On the next page I go a little deeper...