Ken,
Light grey smoke is an indication of incomplete burning of fuel. Suspect either a new nozzle is needed or the alignment of the electrodes is off. In either case, you'll need to access the burner. I'd go for the nozzle replacement if it's been a couple of years since last done. You can also adjust the electrode at that time. I doubt you changed the electrode alignment with your hammering.
As to coolant loose, check around your "radiator cap" on the HH. It can leak slightly and the antifreeze doesn't show on top of the unit, but runs down the back of the HH under the external box skin. Use your finger and check under the rubber gasket around the cap.
Also, check the area near your coolant pumps. The fittings that route antifreeze through the bulkhead above them can crack and leak slowly. There is a check valve there for each zone. Your hammering may have freed up a stuck valve. If leaking, you can replumb w/o the check valve and the unit will work just fine.
Finally, check the plastic line from the plastic expansion tank to the unit. It can get brittle and leak, but since the unit is warm/hot, the antifreeze "disappears". I replaced mine with rubber vacuum hose.
Good Luck. Steve