I've got what I hope is a straightforward central heating question:
My house has a pressurised hot water system, based on a Heatrae Megaflo unit. I've only lived with vented systems before, so I'm not familiar with how closed systems work.
Above the Megaflo, connected at the top of the boiler/radiators/tank hot water circuit, there's an expansion vessel. This has a pressure gauge on the bottom that's currently reading approx 1 bar. There are two other connections to this expansion vessel. One is to an overflow pipe, and the other is to a flexible hose that's connected to a cold water pipe with a tap on it. The tap is currently closed.
So it looks to me like this tap is for topping up the system. What I'm not sure about is under what circumstances I'd need to do that ? Also, what is the pressure gauge on the expansion vessel for ?
Any advice gratefully received,