Here is our crazy setup we inherited from the previous owner when my grandmother bought the house in 2005:
[Linked Image from electrical-photos.com]

The heart of the system is a standard natural gas water heater, I guess 200l. It supplies hot water to both shoerws, bathroom sinks and the kitchen sink, as well as heat via the green circulation pump at the very top of the picture. Further to the left there is the heat exchanger (silver box) that separates potable water and heat.

There are 3 heating zones. Two supply different parts of the house with heat using copper pipes snaking through the brick walls (rather than radiators).
The third "zone" is one long run of straight pipe that runs through the whole perimeter of the house just above the floor, with the intent of battling rising damp by heating the walls and evaporating any moisture inside the walls (so I was told).

The drying circuit is driven by the left-hand pump and controled via a thermostatic valve.

The two heating loops are conencted to manifolds, red and blue, indicating hot and cold but perfectly mixed up. The pump (pretty much hidden by the manifolds) just pumped hot water into the cold manifold, bypassing the entire loop.

In short dry words that means the whole system worked merely by accident. We since had the heating loop pump removed and the original drying loop pump connected to serve both loops.

The pumps used to run 24/7/365 and the only means of control were two thermostatic valves and the hot water temperature. We connected the pumps to a timeclock and only run the heat for roughly 2-3 hours a day depending on the time of the year, which hopefully cuts down on our gas bills drastically. Note how the original genius just hard wired a power strip and plugged in the pumps...

Eventually we might wind up adding radiators though I guess. The wall heati system is nice as the walls get an even temperature, but it takes at least a full day to get the house warm. That's intolerable for a weekend home during the cold season. We usually rely on portable electric heaters and the wood fired tiled kitchen stove until the gas heat picks up.