When the heating is switched on it takes ages for the downstairs radiators to heat up. When they eventually do, they are not as hot as the upstairs radiators. I have bled them and actually drained the system without any improvement. The hot water can be boiling from the taps but the radiators only warm.

jim, October 2009

It may be that the upstairs rads are stealing all the heat and the circulating water has cooled down before it reaches the downstairs rads. If you shut off all the upstairs rads and see what happens you will have discovered something. Balancing the rads might be a solution - you might also be able to speed up the circulating pump to get the water around the system a bit quicker.

http://www.miketheboilerman.com/balancing.htm

Peccavi, October 2009