Water level problems

Hey everyone, hope all is well.

We replaced a steam boiler last year, and I’m looking for some guidance on a recurring low-water issue. The original boiler was oversized by approximately 80 square feet EDR. The replacement is closely matched to the connected load of 938 square feet EDR, possibly slightly undersized. All the basement steam piping is insulated, and the system heats the home extremely well.

After approximately 20–30 minutes of continuous firing, the water level drops enough to trip the low-water cutoff. The default VXT feeder’s time delay allows the condensate to return before it adds water. After about five minutes, the water level recovers and the boiler resumes firing. The boiler heats the home extremely well even though it trips on low water.

I’ve skimmed the boiler multiple times and also cleaned it with a wand, but the issue persists. The wet returns were replaced approximately four years ago. I’m starting to wonder whether the replacement boiler needs a reservoir tank to provide additional water volume while waiting for condensate to return.

Some background on the system and installation

Two-pipe vapor system originally equipped with Haines Vento radiator traps and graduated radiator supply valves.

Radiators on the first and second floors. All radiator traps were replaced when the wet returns were replaced a few years ago.

Six ducted indirect heaters in the basement also serve the first floor. These sit approximately 2–3 feet above the boiler’s normal waterline.

Each indirect has a steam supply and an untrapped condensate drip into the wet return. The indirects are vented through crossover traps connected to a dry return above the heaters.

Vaporstat set to 10 ounces. The 0–3 psi gauge rarely shows any pressure.

Boiler piped with a 4-inch drop header.

Boiler water pH approximately 7.

How do i determine whether the boiler needs a reservoir tank or whether additional skimming and cleaning are necessary? Could the indirect heaters’ piping arrangement contribute to delayed condensate return?

Thanks for any guidance.

Paul