windyhill4.2 wrote:Boilers don't generally go much over 200* & 30 psi ,do they ?? Have to plan our situation when we do switch to coal.
Boilers typically pop off at 30psi and operate at 200F or below (water temp). The problem is, what happens when it goes over those numbers...you need to have tolerance for temporary spikes in those numbers. Without some cushion, you will either be just fine if you never have a problem, or you will have a 'catastrophic failure' (sudden and significant failure) such as piping failures.
Back to OP...
What size pex did you have underground, and what size is your main loop? Did you design and install the plumbing system? I am curious about how you are running and distributing your heat. Main loop, heating zones, etc. Why? If there are size/volume issues, you may have some flow, pressure, or btu issues that stress your system, possibly contributing to mthe recent failure.
PEX can be fine buried, if it is done properly and within tolerances (mostly temp). Iron would work, too, but you lose the freezes tolerance of pex. I would personally avoid copper for that section It has higher heat loss and doesn't have the strength of blackiron nor the tolerance for cold of pex.
Whatever you choose, you will want to take the time to dig, prepare, and insulate a proper ditch and conduit. As mentioned by others, foam and waterproofing as well as crush tolerance (we have a lot of clay here with a lot of rock, so earth movement and hydraulic soil is a serious consideration for us on anything in the ground).
What kind of main loop do you have? Is the underground section part of it? What was the diameter of your main loop/underground pex?
Sorry to hear you are under the weather while your system is down. Hopefully this mild spell will give you time to recover.