central heating only works when hot water on

[miranda]

Hi guys, Since the cold weather has start to come, I have turned my heating on and the radiators only get hot when the hot water is warming up. Once the water reaches temperature the radiators go cold.
I have bled the radiators and nothing changes. The problem is I dont use enough hot water to keep the radiators on.
Help
Miranda

[marrtin]

Does the pump continue to run after the hot water goes off? Could be a faulty zone valve. Try operating it manually.