Why does hot marine come out of the overflow surrounded by my crucial heat system? ...

There is cold (winter) nouns coming from lower...
Answers:    If your heating system have an expansion tank on it the bladder surrounded by it may be defective leaving expanding (expands when the grill comes on) water no place to stir, except out a pressure relief stopcock. When the heats turns rotten and cools down the water contracts dropping the pressure within the system and at that point there is a stopcock that will let hose down in to carry on the pressure the system is supposed to have starting the cycle over again. I am not sure of adjectives the particulars of your system but this is one clear-cut possibility.
We hold dual sinks surrounded by our bathroom....
It could be a defective overflow valve or a defective thermostat. Overflow occur if the pressure or temperature is too lofty, it's a safety contraption so the boiler doesn't explode. Get it checked out by a professional.