THANKS much for such a quick response. Today, when I go home, I will do the following and reply tomorrow:
(1) Shut the toilet shutoff valve completely. Might drain the system first, before doing so.
(2) Look for Pressure reducing valve - Dont think I have one. Where should I look for it??? Inside the house or outside.
(3) Where exactly would I look for back water nipples at the heater???