Radiator bubbling, over pumping

[xxxxx]

I have had 5 new radiators and 3 pumps fitted to my system over the last 8 years. Each fitter conradicts the other - I am so confused. The last radiator was fitted (as usual due to a leak) a few weeks back. After this the radiators seemed not to heat up, so my uncle drained and balanced the system, something none of the fitters have ever done, they just say my system needs powerflushing at a cost of £600. After this, the system worked very well heat wise, but was so noisy I could not sleep. In one radiator next to my bed it sounds as though there are bubbles gurgling every 10 mins or so. I thought it was air but top of rad is hot and no air comes out of bleed valve. I went up to loft to put fernox in to remove sludge but found the expansion tank to a) have hot water in it and b) about 2 inches of an orange kind of silt at the bottom. I called my uncle and he said I should turn the pump down as this was the reason the water was hot. I turned it down from 4 to 1 and the water is now cold in the expansion tank. Does this mean for the year or so my pump has been set to 4 it has been pumping over all that time. British gas set it to that. Is this also the reason for the 'silt' (or is that what sludge looks like). How did it get there? What can I do to get rid of the noise. Now I have turned the pump down I also hear knocking sounds which had dissapeared when the pump was on high. Also, the boiler seems to go on and off a lot rather than be on for a long period of time - is this normal?

 

[kevplumb]

the silt is rust

 

[bathjobby]

Need to put cleanser in the system for a week, drain down and then refill, putting an inhibitor in.

 

[DP]

Your system is plumbed incorrectly. Pump speed should not result in pimp over. You may well not get any pump over with CH on, have you tried run system in HW only mode?

What have lying in your header tank is system components like pump and radiators in form of rust.

I would start with corrective measure by installing items like pump, vent and feed at the correct location followed by system cleanse using chemicals. Be warned that the system may start weeping or even leaking due to introduction of essential cleaning chemicals.