First, while you can heat the water in the indirect that high, it generally isn't required or wanted, but it should have a tempering valve on the outlet to prevent that excessively hot water from ever getting into the distribution pipes...generally, these get set to around 120-degrees. My indirect is set to 140, and then there's a tempering valve which limits it to 120.
The flame sensor may not be working properly on your boiler. Or, there may be a failure in either the design or operation of the circulation and something (maybe the high-temp limit switch) tripping, which causes the boiler to shut down.
A typical cycle is:
- activate the igniter
- open gas valve
- sense the flame is on
- run until either the high-limit is reached, or the call for heat is satisfied
- sense the flame did not come on
- shut off gas valve
- purge the burner of raw gas
- try again (i.e., start over, which may have a limit of repetitions before it quits)
The controls that determine what temperature the boiler runs at is determined by the controller. Often, it will hit that 180 or so when called for heating the indirect. Otherwise, it will only go high enough based on the controller to heat the house. That temperature can be affected by the outside reset, and the programming set points. The type of radiation you have can affect the best temperature.
So, it sounds like there's more than one problem. Ensure the system water pressure is correct as well, and maybe purge air from the system, as that could prevent the water from circulating. If you have a primary/secondary loop system, and the primary pump fails, the high limit switch will quickly shut things off. If the secondary loop's circulator(s) aren't working, there will be little heat transfer to the heating loops (there may be some convection, but it just won't circulate per design).