Advice sought re gas heating

[Nero]

Evenin' all.

Well, wouldn't you just know it. Get back from winter sun jaunt to a central heating system that is working but not that well. The rads upstairs are warm, the thermostat is set at 21C, the boiler temperature to 60C yet the rads downstairs are still cool, even after 3 hours being on. It's been like this on and off for ages. Any idea waht could be the matter? FYI, the water tank is upstairs and once the rads get warm, they get really warm. Help! Nero

[lozzyloz]

You need to tune your rads. Close down (but not completely) the valve on the warmer rads so that some of the hot water bypasses the warmer rads and goes to the cooler ones downstairs. Assuming the system has been bled for any air in the system.