This hydronic system was not working when we bought our home. The fan would kick on with a manual switch but when you changed the temperature settings to go above the room temp nothing would happen. So, no guarantee that this would work anyway. I took a picture of the original thermostat configuration but it's been so long that I cannot find it, so I consider it lost.
I'm pretty sure this drawing is right, I'm not an electrician or engineer. The red, blue, and yellow leads all run to the thermostat. I'm really unsure about the black and white 120 VAC leads that come off of the transformer so I didn't add them to the drawing. However, the fan and pump do run if you jumper the leads all together, so... there's that. I assume they just need to be wired to the thermostat correctly. The pump is a Taco 006-B4 Bronze Circulator Pump.
In any case it seems to me that the 24v secondary off the transformer has two leads: the red, which goes straight to the the thermostat, and the brown, which feeds both relays and has third that I suppose could be used as a C-Wire?
It seems to me the 120 VAC black lead feeds the relays in series to the heat pump and the 120 VAC white lead goes directly to the hydronic impeller and fan.
My assumption is the blue lead (E130 relay, left) control the fan, and the yellow lead (E1305 relay, right) controls the hydronic impeller... but I may have it backwards. I drew the diagram from pictures that are not as detailed as I would like and these wire are a significant pain to get to so I would prefer to solve this with what I have.
So my question: how would you label the yellow, red, and blue leads?
Relay 1 is a Products Unlimited/Tyco 9400-13Q101 relay:
Relay 2 is a Products Unlimited/Tyco 9400-11Q101 relay: