Yes, water heater drain valves can be removed and replaced, and often recommended as the plastic ones that come with them are prone to developing leaks.

well the plumber who installed it says its not the drain valve but the heater. luckly it was under warranty however i have to pay for the labor.

i noticed there is no expansion tank. i asked the plumber and he stated since i am on a well system the pressure tank can act as the expansion. not sure whether thats the case

9 years is fairly soon for the indirect water heater to go bad. Those type units are usually some of the longest lived options for water heaters. Weil-McLain estimates they should have about a 30-year life span.

Before you spend a lot of money to replace the current system you may want to have our water tested to determine if minerals or acidity may be corroding your plumbing, which would lead to premature failure of anything you install.

You can see a life-cycle cost comparison of different water heating choices at the link provided.

The indirect water heater with a high efficiency boiler can be one of the most cost effective solutions you can get. Why don't you want to stay with that and repair or replace the leaky unit?

Since you have a gas boiler then the next best option with regards to life-cycle cost is a high efficiency on-demand pilotless gas unit.

Gas prices are going up so it might be more cost effective to install an electric on-demand unit, but you would probably have to run a higher current circuit for it.

The standard gas and electric tank water heaters that made by galvanized sheets are relatively inexpensive to install, but they are very inefficient and would be more costly over time.

Here is a link that might be useful: galvanized sheets