I don't have an answer to your question, but I have several irons that used to do that. From that moment on, I decided I will never put water in my iron. I use a mister like hairdressers use (got if from Amazon, !)

I removed a rust stain that was caused by a metal embroidery hoop that was left too long. There is a product in the cleaning products aisle--Whisk. It works.

I can't remember the name of it. It was very descriptive in the name. It was near the spray starch and laundry products. I have used CLR because it is gentle on surfaces. But, now I do it like this.

https://www.thespruce.com/how-to-clean-an-iron-2146972

Rit is a product that has a rust remover, a color remover etc. Several different small boxes with either fabric dyes, 'yellow' remover & 'whiteners'. I find mine in Wally World in the laundry dept. near starches & pressing stuff. Usually a powder yhou add to the washer.
Good luck
sewverybusy1

I need to correct the name of this product It's Whink.

Thanks for the vinegar tip!

While staying in Florida last winter, a guild member showed an old quilt (1930’s) wherein the white of the quilt was pure white. She explained that the quilt had had many large brown spots. She had soaked the quilt in the bathtub using a product called “Restoration”, changing the water often. Said the water was stinky and ugly. She continued changing water until the quilt was clean. She had sloshed it about by hand. The results looked as though the quilt was brand new. She had purchased Restoration from the internet.

We didn’t see before photos, but the end results were amazing.