I agree with whereswilbur you see some amazingly cr*p DIY jobs out there, a lot of boilers we replace are the £400 B&Q jobs someone mentioned earlier lol, customers just can't seem to understand that you pay for what you get with boilers, yes sir that worcester bosch will cost twice as much but it will last 20 years not 20 weeks! Also cleaner will remove some debris if left running round the system then drained off and re-filled but if you say have cold spots on your rads because its so bunged up then you do need to powerflush, the only cheep alternative would be to cold mains flush but this is only possible on a sealed system and you still have to know what your doing.