Sounds like it. is it a closed system? Should be a top up somewhere.
It's not, and that's probably the problem actually...
We've got a water tank which fills the hot water tank when it's used for washing up, showers etc.
The radiators are only on when we put the central heating pump on which circulates water from the hot water tank, through the radiators, through the stove, and back through to the hot water tank. So the stove can give you all the hot water and heating you need, but when you use it some water will be taken from the system before being replenished by cold water and repeating the process.
It's probably somewhere in this that's not working, thinking about it more...
