If your radiators are not heating up properly, a power-flush would be highly recommended. Symptoms to show that a power flush is necessary include radiators hot at the top but cold at the bottom. As a result, sludge could be creating blockages in the radiators or pipes.
The older the system, the more likely that there will be sludge in the radiators, this will result in higher heating bills as your heating system needs to work harder to keep the house warm.
Sludge can also damage boiler, heat pump and valves. Radiators slide is a mixture of rust and dirt. This builds up over time and gathers at the bottom of the radiators.