You have a cold water pipe feeding into the coil on the boiler, and a hot
water pipe exiting the coil. Somewhere at that location should be some type
of mixing valve, so you don't get 180 degree water flowing through your
domestic pipes. If it is off and not allowing any cold water to mix, the
problem is with the coil.-

There is a tie valve between the cold input and hot output of the
coil, I am assuming this is the mixing valve to mix in the cold water.
This valve right now is off, why I don't know, but in any event why
would the coil be the problem if the valve is off? Are you saying
maybe the oil company turned off the mixing valve to compensate for
the coil being dirty?
Regardless, if I'm getting "full strength" hot water out ( mixing
valve off) theoretically I should have more HW than if the valve was
on, so that's why I suspect a bad coil.