I just dug the ol' expresso machine out of the back of the cabinet after
a couple of years since it's been used; dusted it off, filled it with
water and tried to use it. The heater works, the pump works, but no
water comes out. t's plugged up with scale somewhere.

I put a pint of water and a 1/2 tsp of citric acid in it and let it sit
for a while and tried it again. No joy. I took the screen off and it
was clear. I notices a stainless steel bolt (looks like a big
carburator jet) in the middle under the screen. I unscrwed it with a
13mm wrench and it is obviously plugged up. I turned on the pump with
this jet removed and it works.

I have the jet (online parts store calls it a boiler valve) soaking in
some vinegar, but I don't know if that'll do it. The valve looks like
it would come apart with two 13mm wrenches.

Is this something that will clean out OK if I just give it time in the
vinegar (or citric acid)? Will I ruin it if I take it apart? Will I
ruin it if I use something stronger, like hydrochloric acid (diluted
50%)? I also have phosphoric acid, which is safer for stainless steel,
but I dunno if it will remove calcium scale.

Worst case is I have to buy a new valve for $20 plus shipping.
Wha'd'ya think?

Thanks,
Bob