Will this break my central heating? pump question.

Here's the background.

Moved to a new house built in the 80's with a rubbish central heating system by the looks of it. It has a conventional boiler (new-ish) with various rads connected with micro bore pipes The entire system seems to be full of sludge 2 of the rads didn't get hot at all due to blocked pipes and many of the rads have cold spots, meaning the house takes ages to heat up if at all.

I've been reading similar posts from this forum and have come to the conclusion that i'll probably need to pay a plumber to power flush the whole system. Before doing this I have tried using chemicals to desludge (sentinal x400) which has semi worked in that 1 of the non functional rads now works.

My next job is going to be unblock the pipe, was thinking about connecting a hose pipe to the blocked pipe by removing the rad then blasting it with mains water? Not sure if that is a good or bad idea? Next i'll need to drain the whole system down to remove the chemicals and hopefully the sludge too. But in the mean time i have 2 questions

1> The boiler has a thermostat limiting the water temp for the heating sys, can I simply turn this up to the max to try and get more heat out of the system or is it not that simple?

2> On the central heating pump, there is a switch on the side with 3 positions 1, 2 and 3. It's currently in the 2 position. I'm guessing it's a power setting to control the flow rate? Is there any harm in me switching it to 3 in the hope the extra flow might shift the blockage, or at least circulate the water quicker so the rads get hotter quicker?

Sorry for waffling, thanks in advance for any suggestions (sensible ones )

AL

See FAQs for a link to the mains water flushing process.

Turning pump up may help distrub some more muck.

Also how well balanced is the system - close the rads that get hot first to see if that helps the ones that don't get hot - if so adjust the locksheild valves on these to get flow through the others (water tries to take the path of least resistance - so rads closest and on the same floor as the pump have an advantage).

Thanks for the quick reply stevesey.

I've whacked up the pump speed for a while to see if this makes any difference but what about adjusting the boiler temperature? Are there any probs with having it set too high? We don't have kids so not worried about burnt fingers on the rads

I'll turn the temp up later and see what happens.