I have an open vented stored hot water system (indirect) and water has recently started venting into the F&E tank as soon as the boiler fires. Water in tank becomes hot and is obviously being circulated. Radiators are all heating up and boiler thermostat is set to approx 65deg. Pump is set to no 1 (lowest setting). Why is this? Are there problems with connecting the feed and expansion pipes in the airing cupboard (I realise that this won't address the cause but would seem to solve the problem)? Any advice gratefully received.