i was on a job today that has a non-bladder type expansion tank. The PRV has been seeping (homeowner thought water was coming for his wall) The boiler pressure was below 20psi when i arrived.Water was seeping out valve continuously. I replaced valve and restarted boiler. The boiler heated and pressure rose above 30psi(PRV setting is 30psi) and valve began to open again.I shut system down and drained expansion tank. The tank installation seems odd. The water feed station is teed into the expansion tank line that is connected to bottom inlet on boiler(Viessmann Vitola).I think the expansion tank should be teed into the supply outlet line from boiler. Any suggestions? This is a 5 year old installation. The expansion tank was not flooded. Im checking back with homeowner in morning.