Greetings.

I noticed today the well pump was kicking on WAY too often, so I went down to look at my system. I noticed the water is flowing through the system at about 8 GPM, but the system was not running at the time. There seems to be a problem with the value not turning off. I didn't have much time to troubleshoot this issue, since I had to get to work. I'm wondering if I reset the system, if that will have any effect. I also still have to check the flow rate of the system when it's on, I seem to remember somewhere around 10 to 12gpm, 8 GPM seems too low.

The value is a TACO 557-2, it's about a $200 value, seems more for commercial or industrial applications. Is this over kill for a Geothermal system? Just wondering.

That is a heat motor zone valve. Heat from (typically) the signal voltage from the thermostat heats a cylinder of wax, which expands and turns on the valve, a process that can take up to a minute and a half. After the thermostat is satisfied, the thing cools down and the valve closes. If yours isn't closing, there could be an obstruction in the line at the valve, preventing closure. I have one like yours (different model) on my system, and although it works just fine, shutting off when the thermostat is satisfied, I do wish I had installed a different one. Taco has a new series, their Zone Sentry, which uses a capacitor-driven electric motor to operate the valve. It opens and closes in much less time, like 5-6 seconds, and draws less power when active. There is a special version for use with well water, perhaps different metallurgy. If I ever have to replace my valve, that's what I will use.

If the water pressure is too high, like >20 psi , then you might have trouble with these. I would recommend the ball valve version. These were made for 15psi boiler loops, not open loop geothermal.

Since the system is still under warranty, I had the installer come out and look at it.  He said the water corrodes the value, he attempted to clean it, but it's not really working any better.  He didn't have a slow close value in the truck, he'll have to order it and return. I think I'll let him change it, see how it's done and get a spare value and replace it again in 3 or 4 years myself.  I also want to get them to back-flush the system. He said it take a couple of hours to do, the system is 4 years old, I think it's due.

Taco specially specifies the 557-G value as a Geothermal value. I'll have to take another look at the serial numbers on the value, but it's orange just like the photo on there website.  I'll ask them about the zone security zone value, it has to shut slowly, to prevent the pipes from moving, but I think 5 or 6 seconds is slow enough. I found this information on the Zone Sentry value: 
 

CUSTOMER CARE

A:

This valve is only recommended for closed-loop systems. It will rust in an open system. You may want to take a look at Taco's geothermal zone valves, which are designed for use in open systems

Yes, the orange 557-G say for geothermal but if you read the specs, I don't think they can handle the pressure. If you put a pressure reducer before the valve, it will work. Just one person's experience. One data point. I am sure you will get many here.

I was just looking at pressure reducers, from what I can see, it appears to constrict the water flow, I assume my two PVC shutoff values on either side of the value and flow meter would provide the same function. I close them both to a point to get the water flow down to around 12 to 16 GPM.

actually, I looked and the spec says 125psi is max for the 557-G but 6-10 gpm is the normal range for flow. I don't see a max flow rate. I do know that we had problems with these and stopped using them. They only worked when the flow was reduced before the valve.

The plastic globe or jar-top style irrigation-style valves from the lawn-sprinkler section of the local big-box hardware store work well, for a lot less $$, with a lot less hassle to get a replacement one if the valve ever fails.

In an earlier thread:
http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/80242/afv/topic/Default.aspx
I discussed the Zone Sentry valve. From that thread: "Per Taco, they have a version for an open loop system (ground water), their part number V075T2B1ZA024Q4A1." That number came from a discussion of this with Taco. I first got information from their website for a Zone Sentry valve of the right capacity, but later Taco advised me of the slightly different version, for use with well water in open loop.