pressure in boiler getting too high
Do you have an automatic fill valve? Is there a manual valve in line with it? Try closing the manual valve if there is one. If that solves your problem, adjust and/or replace the automatic fill valve.

If you have a (domestic/potable) hot water coil, that could be leaking into the boiler, too. Shut off the domestic hot water supply on the cold side of the boiler to diagnose that possibility.