Ok so their is a boiler and the PSI is rising and rising until the temperature and pressure releif goes pop. My friend who is a Master plumber thinks its the coil of the indirect has pin whole leak and it allows pressure from the house into the tank. Now he doesn't vocalize much so im not sure how he got to this conclusion. I was looking through threads below just for kicks and saw that a guy was expercing a similar problem with thermal expansion and setting off the pressure relief.
SO i guess my main question is how can you tell Its a leak in the coil i couldn't figure it out, Also how does the house pressure then effect the boiler? I would think if anything would'nt the leak kinda make it like an open system the thermally expanded water could flow into the indirect and then out into the house. Or is this just not feasible due to the pinhole could never handle such a large increase in water volume