Gravity Central Heating

[chotu]

How does gravity central heating work? My buider says it is not possible to have hot water independently, you have to switch on the immersion heater if you require hot water alone. The corgi registered engineer that came to service my boiler says the opposite i.e. it is possible to have heating+hot water or hot water alone in a gravity system. Who is right?

[JohnThorn]

The Corgi guy is nearest. Gravity CH relies on convection to move the water around the system instead of a pump. It needs bigger pipes than a pumped system. A pumped system usually has two valves - one for hot water and one for CH which work independently. Some systems are hybrid where the HW is by convection and the CH pumped. You can have hot water independently in a gravity-only system - but you have to turn off all the radiators separately.

[GeorgeR]

It only works properly if the radiators are quite higher than the boiler. You could have thermostatic valves on the rads to keep them off when not required.