I have a old GM Delco Heat Boiler Furnace in my house, and it builds up excessive pressure, and then releases it. This happens repeatedly.

Burner not turning off on the control. Change to lower temp setting. Check for defective control.

Plugged expansion or full tank. Drain tank and refill boiler.

Defective pop off valve (safety control ) replace if unit is running at correct pressure and valves opens.

It is past its prime. You may want to consider getting a more efficient unit.

Pressure cold? Pressure hot? Could be a pressure reducing valve or expansion tank problem. Might want to get a pro.