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I am thinking that one of the relays on that board are acting up. there are seven 24 VAC coil relays and one 120 VAC coil relays. I believe the one with the metal strap all the way to the left is the 120 VAC relay

Grainger sells the replacement relays for that board. Grainger # 6C875 is the 24 VAC one. Grainger # 6C876 is the 120 VAC coil relay. But it has been so long since I worked on that older model. I can't be sure if my information is current. I thing one of the 2 relays on the left are the problem. and it looks like that problem has happened once before and someone robbed zone 4 relay and swapped it to fix a problem in the past. Just a guess.

If you can give up one of the zones for now and you take a zone relay out and swap it with the second from the left relay, you may solve the problem. Then you can order the #6C875 from Grainger to replace the failed relay.

@SteveSan From TACO Tech Support is on here regularly, and he will know if one of those relay cubes will solve the problem you are describing.

" I also measure the voltage of the relay coil terminal when zone 1 is called. The coil of ZC ZR got high voltage (~14V) to activate but all other relay coil including zone 1 got low voltage (~0.8V). "

The 14 volts measured without even the load of the relay coil in the circuit may mean a poor connection, a relay contact that is tired, worn or oxidized or an oxidized switch contact from never being used. The 7 relays are 24 VAC coils. There is not much on that circuit board, it it was a poor solder joint you probably could physically agitate it by flexing things.

I would use the ohmmeter function to test the NC contacts of the 120 VAC relay, then verify the coil is 120 VAC and if you can safely apply 120 VAC to the coil and test the NO contacts.

OK. it is getting late here and I don't want to miss Santa's visit:

In order to get heat for tonight, connect all the circulators to operate constant. set one of the thermostat to call for heat so the burner will run. when the thermostat is satisfied, the burner will shut off and the boiler temperature will drop as the circulator pumps move the water thru the system. You can do the same for the DHW circulators. Once you charge the tank with DHW from the boiler, you can disconnect the circulators so the DHW does not get too hot.