The boiler is flooded
Don't blame the automatic water feeder; solve the surging problem by cleaning the boiler, adjusting the firing rate or correcting the improper near-boiler piping.
When motorized valves close, you lose that "leftover" pressure at the ends of the mains. The static weight of the returning condensate alone usually isn't enough to overcome the pressure in the boiler, so the water backs out of the boiler. If there's an automatic water feeder, it will open and add water to the boiler. The next time the motorized valve opens, the condensate will flow into the boiler and flood it.
If you use motorized zone valves with a gravity-return system you also must use a boiler-feed pump and end-of-main steam traps.
When the steam bubbles condense, the water in the boiler will fall to a point lower than the water in the gauge glass. The water in the gauge glass offsets this by falling into the boiler. If you have an automatic water feeder, it will open and eventually flood the boiler.
This type of problem is built into the boiler design, and it's tremendously aggravated by dirt. You can sometimes cure it by underfiring the boiler. Underfiring produces fewer steam bubbles, giving each more room. But don't underfire to a point where you'll only be simmering the water. Also, make sure the boiler is as clean as possible.
Correct the pH with chemicals. Ideally, it should range between seven (neutral) and nine (mildly alkaline).
Check the feeder by doing a broken-union test. Bring the boiler water level to the "feeder closed" point. Open a union on the outlet side of the feeder, below the boiler water line. There should be a gate valve or a ball valve after the union to keep water from flowing from the boiler. If the feeder is tightly closed, no water should flow from the union.
If you supply the feeder with hot water, lime scale will accumulate on the feeder's seat and eventually cause the feeder to fail. Feeder manufacturers recommend you feed only with cold water if you want to avoid this problem.
You can check this by doing a broken-union test. Bring the boiler water level to the "feeder closed" point. Open a union on the outlet side of the feeder. Now open the gate valve or ball valve between the union and the boiler. If the line is clear, you should get a steady flow of water from the boiler. If all you get is a trickle, change the line.
Clean the check valve, or remove its flapper. If the gravity-return system has an equalizer, you don't need a check valve.
The steam boilers of yesteryear were different from the ones we're using today. One outlet may have been enough in the old days because the boiler was much larger, had wider sections and a more generous steam chest. A boiler of the same rating nowadays, however, may need two or three outlets to dry the steam and balance the water line.
This is why it's so important to read the manufacturer's installation instructions and follow them. If you pipe the new boiler the same was as the Dead Man piped the old boiler, you're probably going to get into trouble. Read the boiler manufacturer's instructions thoroughly, and follow them to the letter.
Educate the building owner on the right way to feed a steam boiler. Don't add water by hand unless the boiler is off and the condensate has returned from the system.