The first thing to do is to check that the lockshield is open. Have replaced thermostat but to no avail. How To Drain A Central Heating System Justboilerscom Try turning all the valves off on the rad's upstairs to see ifyou get any heat downstairs, probably as gas4you say's the pump is on its last legs and because heat rises thats why your rad's upsatirs get hot even though the pump is in your outhouse Central heating not working upstairs . A zoned system is simply a single air conditioning/heating unit that uses two thermostats and dampers within the actual duct work. In this article, we’ll explain what you can do to fix this problem. If your boiler works but the radiators are not heating up, then the likely cause is a faulty boiler pump or your central heating controls. Typical causes are seized valves, blockages, an imbalanced system, or the presence of air. This is a valve on the side of the radiator with a small plastic cap. This is most likely caused by...