central boilers ashtrol

how important is Ashtrol to use in the fire box? (furnace firebox pH
modifier).

Depends on who you ask. Ask the dealer or the company and they'll tell you that you void your warranty if you don't use it.

Ask some other users and they'll say it is just a way to get you to spend more money.

Here is what I did.

Before firing the CB I laid down a layer of ashtrol on the bottom of the fire box. I then lined the bottom and the angled sides with fire brick - a friend with a CB recommend this. And then when done with the bricking I filled in the cracks with ashtrol.

Then I didn't add it again. Although I sold the CB a few months later.

My friend has had his for years and has not had corrosion issues and doesn't use the Ashtrol.

Good luck.

Pete