I have two Maple Chase 9600 thermostats in a two zone system. Neither the air cond. furnace, or fan will come on. There is power to all units. Fuses are intact. The problem started a week ago (after 9 years of flawless use). I replaced the batteries and reset the thermostats. While reprogramming the thermostats, the air and furnace began to work again, but a week later the thermostats cannot activate anything again. Any suggestions for tests to isolate or fix the problem?