Hiya everybody, I've only got a limited knowledge of plumbing, so I'm sorry if I leave out any important details! I'm wondering if anybody out there would know why the water in my F&E tank overheats so readily? We have our hot water to come on twice a day for half an hour each once in the morning, once in the evening. On a frequent basis, although not every day, just before the hot water is due to go off in the morning you can hear a rumbling noise from our F&E tank and it fills with hot water. It is virtually always at this time. The water had been gushing out of our overflow pipe until recently and we've only managed to stop it by adjusting the position of the ballcock so that the tank isn't so full. A week or so when this happened, air obviously got into our system and some of the radiators stopped working. Our very old Myson CP63 pump was also making a louder noise than it usually does, so I thought it might be a problem with the pump. We've replaced the pump with a Grundfos UPS3, but it doesn't seem to have solved the problem. As far as I know these kinds of things can be caused by several things, including a small hole in your hot water cylinder. However, I thought this steadily caused water to leak into your F&E tank and the water gushes in. Also, I made a bit of a hash of replacing the pump and the F&E tank was empty for a couple of days and no water dripped into it. I thought it could also be a thermostat issue. The one on the hot water tank seems to be working OK. The hot water just came on this evening. Before it came on the thermostat clicked on around 40 degrees, by the time the 30 mins was up the thermostat was clicking off at 60 degrees where it's normally set. We've also tried the boiler thermostat on our Ideal Classic FF boiler. It's currently set to 77 degrees (as it generally is over winter). I turned it down this morning to the summer setting (66 degrees) and put the heating on. The boiler was clicking off before the radiators had heated the house properly, which suggests to me that the boiler thermostat is working OK. Does anybody have any ideas what's wrong? I assume I'm missing something really obvious!