Weil mclain ultra 105

Since you have to "hit the breaker reset" I believe your issue is more than a loss of communications with the thermostats.

Screen color before any reset action ?

Any error messages ?

The circuit breaker trips in the electrical panel, but when you reset it it's fine for one boiler cycle then the breaker trips again?

Turn down all thermostats. Reset breaker. Turn up and check one zone at a time. Check one, then turn down and check the next. Its possible one of the zones will trip the breaker. Circulator?

on my boiler standby is shown when the boiler is at temperature or a no heat call

Depending on piping and control logic, a secondary or primary pump may still be running on a heat call but the boiler does not not need to fire if it is at temperature

So you basically shut off the switch and turn it back on to fire the boiler. Where does "breaker reset" come from? Never mind, don't answer that.

When it's running and providing heat, what does it say in the display? On top it should say "fin tube, or hydro coil" or something to show you there's a heat demand. I mention this because you said only the second floor is baseboard. What type of heat is supplying the first floor and basement, and do those zones work without a "breaker reset"?

That boiler is capable of running multiple circuits at multiple temperatures. So we need to know if the second floor circulator (2 zones on the second floor?) is wired directly to the boiler, or does it go to a zone control panel outside of the boiler?

What thermostat are we dealing with on the second floor? Is it a four letter word?

So the boiler handles 2 heat zones. What makes domestic hot water?

Does the wiring for the second floor circulator go into the boiler or a zone control panel?

It could be as simple as a loose thermostat wire.

I'd start when it acts up (which seems consistent) that the thermostat voltage is present when expected and the power to the UControl module is normal also. You would need a multimeter and measure AC Volts.

I believe the Red boxes I added to the image below are the 4 thermostat connections. Once it acts up I would verify for all 4 thermostats that the 24 VAC exists with no call for heat and the 4 inputs individually drop to 0 (zero) VAC during a call for heat. Also I would verify the 120 VAC at P1 and 120 VAC and 24 VAC at the transformer connector P3 when there is a call for heat and the boiler does not respond properly.

Agree, need pics. You said only 2 zones being used for the second floor. The first floor and basement have mini splits, no radiators or baseboard. So how do 4 thermostats go back to the boiler? There must be at least 2 external circulators. One boiler circulator right on top of the boiler, and a system circulator for the second floor loop(s). Pics please.

In the diagram @109A_5 posted, there should be wires at terminals 1 and 2 on the P15 block. Check the wires and block are secure. Then work your way back with the thermostat wire and tighten any connection or splice all the way back to the thermostat.

If I were to guess, because we've got nothing to work with, I'd say there's 2 zones for the second floor with a zone control panel. The relay that closes XX to signal a demand to the boiler hangs up, so the boiler remains in Standby. Turning the power off and on is like a defibrillator.