This is one in a series of posts and questions you'll eventually see from me about fixing the mess the previous owners left of the geothermal furnace in our house. We inherited a bunch of problems and we're trying to sort them out one by one. I had intended to start with a background post and ask some general questions about a number of things that don't quite add up about this install but a valve failure forced my hand. The ultimate question is about the electrical wiring for a new slow-open/close valve when I think the original install may have been non-standard but I'm going to give you a lot of background info to make sure you have enough to help me. My final questions are: 1) Is there any danger in the way it's hooked up now? 2) Is my understanding of the best-practice way to hook this up correct? The furnace is a Waterfurnace Envision NDV038A101CTL. I am not entirely sure what thermostat is in use. The house came with a stack of manuals, one of which is for an Emerson TP32W03 thermostat. However, the actual thermostat is marked Emerson on the outside but marked White-Rodgers 1F95-1277 on the inside. Looking both up online, they are visually identical but I have no idea if they function identically. The original water flow valve when we bought the house is a quick-opening/closing grey drum actuated by a black solenoid. I don't have a make or model on it because it's in the trash. The valve died Saturday morning. Thankfully, we had already intended to replace the old fast-open/close valve with a slow-open/close valve from Taco because the fast valve was causing severe water hammer. The unfortunate thing was that the death of the old valve pushed me into installing the Taco valve before I had time to learn enough about it to know what I was doing during the install. The original valve had its power wires tapped directly into some fairly heavy gauge wires inside the furnace. The wires tapped are *NOT* on the control circuit board. The only labels near the wires are L1 and L2 and the wires connect to a black box with a small copper coil (like a transformer) hiding behind the black box. The original wiring energizes the solenoid at the moment the compressor switches on, so I suspect the installer may have tapped the wiring for the compressor itself rather than any of the control logic wiring. The new Taco valve is a V075T2G2ZA024Q4A1 GeoSentry Geothermal Zone Valve that opens/closes based off a small electric motor and capacitor. The Taco valve has 4 electrical connections on it labeled C, W/Y, and two for the End Switch. The install paper says C is supposed to be connected to the common/ground in the furnace. The W/Y connection is supposed to be connected to the Y wire coming from the thermostat. The end switch terminals are supposed to be connected to the Y connection from the thermostat on one side and to the Y connection in the furnace on the other side. When Y from the thermostat goes high, the capacitor in the Taco begins to charge. When it's full, the valve opens. Once Y from the thermostat goes low, the Taco valve uses the energy stored in the capacitor to shut the valve. Once the valve rotates fully open, the end switch connection closes and Y from the thermostat is connected to Y in the furnace. Or at least that's how the install instructions say to do it. Of course, the existing wiring doesn't work that way. Right now, the Taco valve's C connection is hooked to the common/ground side of the wire the original installer ran out of the furnace chassis to the valve location. The W/Y connection on the Taco valve is connected to the other conductor from the original installer's connection that shows 24V AC when the compressor is running. On first test, with the capacitor fully discharged, when the thermostat called for heat, the fan started, then a while later the compressor started, which powered up the Taco valve. After 34 seconds, the capacitor in the Taco valve was charged and the valve reached fully open at 38 seconds after compressor start. After the furnace ran and cycled off, the subsequent activation had the valve fully open 19 seconds after compressor start. The furnace did not lock out with a temp error even though the water flow valve opened after the compressor started. So, that's my first question: Is it safe for the furnace to keep starting the compressor 19 to 38 seconds before the flow valve is open? Now, I know that ideally the compressor shouldn't start until the valve is fully open. However, I'm not finding any information about how to change the wiring inside the furnace to get into this configuration. Reading the install paper for the valve, it seems like I need to disconnect the thermostat Y wire from the control board inside the furnace and instead run it to both the W/Y connection and one of the end switch connections on the valve. The C connection on the valve needs hooked to any of the C/ground connections inside the furnace. Finally, the other side of the end switch on the valve needs connected to the Y connection in the furnace (where the Y wire from the thermostat currently is screwed in). Is my understanding of how to re-wire this correct? Thanks for the help guys.