If water level is rising instead of lowering on oil heater unit, is there a leak? Could something worse happen. Oil man had to drain water to lower water, and said to watch it to make sure it doesn't rise again. Any answers much appreciated ☺️
The two most common causes are:
Defective auto-fill valve (most common in steam systems).
The fill valve is similar to a toilet fill valve where a float ball raises or lowers with the level of the water maintaining correct levels.
Leaking heating coil.
Also, a leaking coil within a tank-less or indirect domestic water heater. The coil sits in the furnace and if it leaks, municipal water collects within the furnace, causing an overfilled condition.