Boiler one zone call heat but not fire up
 

I have an 13 years old super hot boiler, only 2 zones.

zone 1: 1st floor heat
zone 2: 2nd floor heat

If Zone 1 works fine. zone 2 not
If Zone 2 works fine. zone 1 not

If zone 1 works fine, When singly turn zone 2 on, I can hear the click sound from boiler, and the 2 circulator pumps water, but the boiler not fire up, if now turn zone 1 on, the boiler will fire up just about immediately.

Any ideas on what I could do to fix this?

Thanks!

Do you get enough heat in zone 2?

Sometimes the zone and the burner are wired and configured to operate independently. When the water temperature in the boiler gets too low then the burner comes on. This configuration could have resulted if the system was originally one zone and the second zone added at a later date.

If zone 1 always turns the burner on, then there needs to be an overlimit switch to turn the boiler off if the water gets too hot. A possible disadvantage is that zone 1 might be forced off before the room temperatures are reached.

Thank you for your answers,
Yes, zone 2 is no heat, but zone 1 can reach the temperature I set.
the 2 zones setup in one sametime.
I noticed the water out temperature is always high, like 180F, if this is the reason, how can zone 1 can fire up in this temperature?

If you turn up the thermostat for zone 2 and turn down the thermostat for zone 1, does the burner come on sooner or later? At what temperature?

You probably have a L8124 or L8148 dual aquastat that has a relay for the zone 1 circulator and for the oil burner also. The second zone is probably wired to an 845 relay that should have been powered by ZC or the 8147 (24) 180 is not awful high for the temperature to be. You can get the wiring from www.taco-hvac.com

Thank you all :)
Now the 2 zones works, a new question comes, everytime turn on the thermostat, it need all most 3-5 mins the boiler fires up, is it normal?

If the boiler was up to high limit temp, yes its normal.