Question from Peter Clough, via email:
My gravity hot water system doesn’t produce hot water. I’ve checked and cleaned out the header tank and checked that the vent pipe is okay. There is hot water going up from the boiler to the heat exchanger in the hot water tank but no hot water coming from the exit of that heat exchanger dropping down to the boiler. I’ve put a bleed value in the ring near the boiler to try and vent any air, but all I get is scalding water from the boiler. Have you got any suggestions?
Answer from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
Nowadays, generally a gravity hot water circulation is only used on solid fuel burning appliances. For many years the industry has recognised the efficiency and performance benefits of pumped circulation of both hot water and heating circuits, so firstly if the boiler is gas or oil-fired I would strongly recommend you upgrade the circuitry to fully pumped.
Taking these comments to one side, the operation of a gravity circulation is normally quite straightforward and trouble free. Have you any thermostatic or motorised valves on the flow or return circuit to the hot water cylinder? If so, then it would be a consideration to check they are free of any contaminants or failure.
Also have you tried operating the hot water system in a hot water only mode? That is with the central heating system turned off and the circulation pump not running. I am aware of instances where for different reasons the heating system circulation can sometimes be the issue leading to the circulating pump partially circulating water through the hot water gravity circulation pipework and “disturbing” the normal pattern.