Gas Burner / Hot water system problem

I've been away for awhile and I came home to an 88 degree house; apparently one of my digital thermostats got stuck "on". I don't know how long its been running continuously.
I subsequently noticed that the overflow pipe on the boiler has a steady stream of water coming out, and its the same whether the boiler is running or not. What could the problem be?
Arnie
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If your boiler is running, you probably ought to bolt it down to the floor.
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