Winter is Coming, Heat is Missing

USN_Retired

I have a new Laars Mascot II Combi unit. I have since learned this was probably a bad choice, so now I’d like to try and make the best of it.
The unit is installed in an insulated garage using a primary/secondary loop setup with a heat exchanger separating the two. Primary side was flushed and filled with water using the internal pump to circulate liquid and remove air then the unit was powered down for the night.
Power was reapplied the following morning prior to the propane service folks arriving. The 24V 2A circuit breaker immediately tripped.
Obviously the unit cannot be tested or fired without control voltage, and the blower runs continuously. There are no visible signs of anything abnormal. My next step will be to remove the control module and open it to see if anything jumps out.
Does anyone have any idea of what the “usual culprit” might be?
Thanks.

Alan (California Radiant) Forbes

Is the 24V 2A circuit breaker part of the boiler? Some pictures would help.

EBEBRATT-Ed

Look around for loose wires, maybe a wire nut came off, Or a wire could be pinched under a cover

mattmia2

Did something leak and soak some portion of the controls?

Zman

Sometimes it is easier to disconnect anything you suspect to be an issue from the controller, replace the fuse and see if it holds. If it does, reconnect the wires until it trips again.

USN_Retired

Alan (California Radiant) Forbes said:

Is the 24V 2A circuit breaker part of the boiler? Some pictures would help.

Yes, the circuit breaker is part of the boiler and is located behind the center panel with the power switch, display etc.
The circuit breakers are near the center and the 2A one is on the right with the white line indicating it is tripped. The left breaker is the main 10A.

USN_Retired

USN_Retired

EBEBRATT-Ed said:

Look around for loose wires, maybe a wire nut came off, Or a wire could be pinched under a cover

No loose or pinched wires, and no missing wire nuts.

USN_Retired

mattmia2 said:

Did something leak and soak some portion of the controls?

There was a small amount of water that dripped from the air eliminator but it was wiped from the tray and didn't contact any circuit components.

USN_Retired

Well folks, I went down the painful road of disconnecting things and reconnecting. No changes so I started chasing wires. Clipped one tie wrap on a bundle that held it to the chassis, and everything works.
I’ve studied that bundle looking for anything. Nothing!!! Maybe some tension on a connector downstream or some other bizarre item? Who knows?
The bundle is nicely tied over its length and seems to lie nicely where it should. I have not replaced the tie wrap but will keep an eye on things.
I’ll get the propane folks out next week to accomplish the fuel conversion.
I’ll keep everyone posted.

mattmia2

i'd look very carefully along that whole harness for a wire that chaffed or cut on the edge of something or got melted somewhere. wen you cut the zip tie something anywhere from end to end of that harness could have moved away from what it was touching. especially look for wires passing through holes with raw metal edges where someone didn't put a grommet back while working on it.