Like many on this site I am trying to install a smart thermostat. I have 3 wires, 24V Red, white, and blue at the thermostat, but only 2 down at the boiler. My boiler is a Burnham Alpine model number ALP080P. I can see where the contractor cut the 3 wires and spliced it with the new wire with electrical tape when we converted to gas from oil. I feel comfortable extending the 3rd wire to the furnace but there is no common, or C, terminal shown where the other 2 wires connect. I have read that I can splice the third wire into a 24V common wire, but I’m not sure which wire would be best. I have included pictures of the wiring diagram and my set up. Any help would be greatly appreciated!
As it stands right now you are not equipped to have a C wire. It is missing. Or you are not telling us all the wires that come out at the thermostat.
Using multimeter find out which 2 wires give you 24 volt.
Or, you will have to run a new C wire from the 24 volt Transformers secondary side to the thermostat