A couple of weeks ago we noticed that the central heating pump was pumping for a long time, when I looked out I noticed that was water was coming out of the expansion tank overflow. I had this problem last year, then the ball cock in the expansion tank needed replacing. I had no end of problems after as I had to drain the expansion tank, air got into the system, which subsequently damaged the pump as well. So we had to have a new pump installed as well. So when it started again last week, I called in the plumber, he says that the system needs to be cleaned to get rid of the crud as there could be a blockage causing the water to overflow. He is going to charge £250 to do this. 
Now this week I found that a couple of the radiators where cold at the top due to air, I have bled these now, but also no more water is coming out of the overflow and subsequently the pump is not continuously on. So my question is have I solved the problem, or should I still get the system cleaned and spend £250 quid?????
Additional info, The central heating water is heated by a Baxi back boiler and is very old, we also have an immersion boiler for the hot water.
Now this week I found that a couple of the radiators where cold at the top due to air, I have bled these now, but also no more water is coming out of the overflow and subsequently the pump is not continuously on. So my question is have I solved the problem, or should I still get the system cleaned and spend £250 quid????? Additional info, The central heating water is heated by a Baxi back boiler and is very old, we also have an immersion boiler for the hot water.
