A week or so ago our central heating remained on after the timer had gone off we manually turned the heating off. After this we had no central heating at all but hot water was working fine. Consulted a plumber who told us the problem was the actuator on the central heating valve which we have since replaced. Now we are getting heat in some radiators (mainly upstairs) but all our downstairs radiators bar one are not getting heat-all these were working fine before we had the initial problem.
Also the boiler will only stay lit for as long as water in the tank needs heating, once this reaches temperature everything shuts off including the central heating. Have you got any ideas what the problem could be?