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Please don't guess.
You need an experienced tech with a meter to find what happened.

Could be something as simple as a loose wire on a terminal, or damaged thermostat wire to the zone board. Check to see if that thermostat wire is continuous (or look for junction box), is broken/damaged/cracked.

Check the dip switches on the board to make sure they are on the proper settings also make sure the board is wired to proper terminals they should correspond with thermostat and dip switches

ZoneFirst w/ Honeywell thermostat not getting the heat call signal

A little more than a month ago I had dual zone installed. I have Honeywell thermostats with a ZoneFirst H32P Uni-Zone Master Zone board. The system has worked for a month. However, now when I make a call for heat on the main floor, the Honeywell t-stat is getting the signal, but nothing happens on the Zone First board. When I call for heat on the second floor everything works as expected. Also I have a whole house steam humidifier that is attached to the main floor t-stat. When it calls for humidity, the Zone First board correctly calls for just the fan and opens the correct damper. It just doesn't make any sense why it just stopped working.