Hi, Could anyone explain what might be happening in my system? I have a sealed gas central heating sysyem (Baxi Solo 3) and Megaflo unvented hot water tank. 4 Hot water taps in the house and a shower off the HW tank. 8 rads in total, small 3 bed terrace. If I turn off the cold water mains and leave over night (with the heating and HW off as well), there is a 'rush' of water through the pipework when i subsequently switch the mains back on in the morning. No tap is turned on during the period that the mains is off. As far as I can tell there is no leak in the system anywhere. I just dont understand where the water can be going. My thought is evaporation from the HW tank but can't see how it would loose much over night? There will be some warmth left in the tank from the previous evenings heating but thats it. Another thought might be the megaflo's internal expansion system being re pressurised but surly this can't be the case as where can the pressure inside the tank go when the mains is turned off?
Thanks
Thanks