Gypsy Girl:

Read my post in the thread entitled "Bleeding Hot Water Radiators - Conflicting Instructions".

In a house where you typically don't have zone valves, but you do have multiple radiator loops going to different areas of the house, the heating contractor will often put in gate valves as "balancing valves".

The purpose of these balancing valves is to prevent all the flow from the pump from going through the shortest radiator loop, and leaving virtually no flow through the longer radiator loops.

It could be that someone didn't know what those valves were for, and simply opened all of them wide open, thinking that doing so would ensure the full flow rate of water through all of the loops.

But, if someone did do that, it would result in almost all of the water flowing through the shortest loop, providing ample heating to that area of the house, but suddenly NO water flow, and therefore no heat, to any of the other radiator loops. So, at least one other area of the house could be cold even though there's nothing wrong with the boiler, or pump or heating system.