Boiler Not Heating | What could it be?

[@kelving.2200]

The second you said they jus got a new tstat, I already knew that was the culprit

[@thomasszilagyi7445]

I had the EXACT SAME THERMOSTAT fail on 2 boiler systems. I installed that useless over engineered "Honeywell Home CT87K1004 The Round Heat Only Manual Thermostat". Do you know that is has a 3v BUTTON BATTERY in it?! I put it in my Father-in-Law's house where it is connected to a TACO zone valve. It did not work. I did the same procedure as you and tied the Red and White together to make sure the zone worked, and it did. I then bought the Honeywell round thermostat to my house to test it. My thermostats are connected directly to a TACO Zone Valve Control unit (ZVC403). The thermostat failed on that, too. Well the thermostat didn't fail, IT NEVER WORKED. Honeywell needs to do better. I installed a basic no-name electronic thermostat for my Father-in-Law. (I tore apart that Honeywell to get to the non-serviceable battery to test it and yes, it was OK at 3v DC)

[@john7017]

When you have 29 volts at TT terminals, you known the thermostat circuit is not closed.

[@HometownHVAC]

@@john7017 Yeah lol Cant believe I let that go over my head, sometimes we gotta get lost in the weeds to learn.

[@northeastMericanNimrod]

He checked for voltage at ff first hahaha

[@petergriffin1546]

Great job. could you have jumped it down stairs to confirm or lead to bad thermostat?

[@HometownHVAC]

@@petergriffin1546 Yes I could have jumped it out downstairs at the Furnace. Just done it at the thermostat out of habit.

[@thomasszilagyi7445]

@@HometownHVAC Better to test the wiring lines from the thermostat, especially after seeing that inferior "clothesline" wiring job flapping in the wind.