can anyone help with this problem please. hot water has started to vent into the expansion tank in the loft, every time the boiler fires up it vents into the tank, not sure how long it has been doing this but have heard the water going into the tank for a while now but only just investigated today. the boiler is a glow worm economy plus in a 3 bed detached house that is 13 years old and we have lived here since it was built. the only problem we have had is a part in the boiler replaced and a new pump about 9 years ago. the boiler is serviced every year. what could be causing this problem? I have noticed people with similar problems in the forum but I am not sure the answers given would solve my problem. Should clarify that water only flows when boiler is on, flow stops when boiler stops.
The problem is most likely caused by a badly designed system. If the feed and expansion pipes where they connect to the system are set too far apart, then either air will be drawn into the circuit or water over pumped into the header. This situation can eventually result in the tank collapsing with inevitable consequences.
Try examining the system to see how it is connected and try turning the pump speed down to see if this improves the situation.
Check this diagram of how a system should be designed.
thanks Plumbbob and steve the gas for your answers, I have checked the measurements against the diagram and they all seem to be as they should be, difficult to see the pump setting, I assume you turn the big screw in the centre, I think it is already on No 1. I can't understand why it has started to do this when I know from previous checks on the expansion tank (though not for some time I admit) that it only held cold water. Have you any other ideas as to what has caused this? Thanks for your assistance.