Boiler: Tranco (can't find model or other info anywhere on it)

Relay: Taco 506-4 (using Taco 007 calculator pumps)

Aquastat: Honeywell l8124a,c

I just finished installing two new zones and a new relay controller on my Tranco boiler and am now in the testing phase. When any thermostat calls for heat through the relay control the isolated end switch does it's job properly and closes the connection (as a dry contact). On the a'stat TT connections I measured that the connection is closed properly and the switch at the top (metal plate that clatters on and off- not sure on the name) closes correctly. At this point I would expect that B1/B2 would be energized and send some power down to my burner, but nothing is happening. I see a measly .05 volts on B1/B2 and even less on the burner contacts.

I know it's a possibility that my aquastat burner control is fried, but I'm hoping it's something more simple. The a'stat worked fine last winter and kicked off properly as expected.

Pics of the setup... Ignore the Hi/Low settings. I messed with them to see if the temp sensor was the issue.

enter image description here

  • 2
    What happens if you jumper past the relay? If that makes everything run normally the relay and/or its installation are the problem, if not you disrupted something else or have the relay connected entirely incorrectly.
    – keshlam
    Commented Sep 6, 2015 at 17:02
  • The only connection from the relay to the a'stat is from XX to TT. I have jumped TT and the metal plate clicked as normal but still no burner ignition.
    – JMD
    Commented Sep 6, 2015 at 17:18

1 Answer 1


The issue ended up being that my aquastat was busted. After exhausting all other possibilities I bought a new one and hooked it up and everything works fine.

I have no idea how the original broke, but it's safe to say that it did.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.