I have Tetco Heat Pump system that came with my house when it was purchased. About a year ago, I started hearing a water hammer in my pipes that I traced back to the solenoid(?) in the picture below. It would continually "click" and cause a small hammer to travel back along my cold water pipes toward the main pressure tank. A small amount of water seeps out at the base of the "coils" when this is happening, as well.

The local firm that installed the Tetco unit is still in business and suggested that I try to bypass this component. The instructions given to me over the phone was that I should be able to open up the top of device and manually lift up a pin.

After looking things over, there's not an obvious way to disassemble the device and I'm hesitant to jump in without knowing more about the device and its function. I did contact a local plumper and he said he doesn't work on heat pumps and referred me back to original installers.

So, can anyone identify the component in the picture and its purpose? Is it safe to bypass and what is the proper way to go about it?

Wide shot of the device in front of the Tetco Close up of the device

Edit: Video of “clicking” and knocking

https://youtu.be/7TYZdOBjJKM https://youtu.be/KHxNaMSR9bo

  • So the local firm said you should bypass it, but they didn't tell you what it is and what it is for? For safety, it looks like there is a good sized spring in there under compression, so don't try to remove the screws until you understand how it works.
    – JPhi1618
    Commented Nov 3, 2017 at 19:35
  • @JPhi1618 Yes, and that was after multiple service calls to figure out why the unit was no longer putting out heat.
    – Lucas
    Commented Nov 3, 2017 at 20:05

4 Answers 4


As per @Lukus , that unit is a geothermal heat pump that is using well water to provide for an approximately 55 degree source water. Wow, what a waste of good water! If the device you are speaking of is the item on the left side with the gray top and the spring it is temperature sensing control valve, probably made by "Johnson Controls", that maintains a given set point temperature, at the sensing bulbs location. (NO, it is not a solenoid valve) . If you bypass this device you will affect the heat-pumps operation, good or bad, I don't know, and you will probably use much more water. A similar model number of this control would be V47AA or AC. AS for a solenoid valve I do not see one in either picture, but there probably is one somewhere. Item last; the people you called that originally installed the unit are probably not the same people that run the company now. Their advice on how to proceed was not in your best interest and shows that they have little knowledge of your installation.

  • I found the matching parts document here.
    – Lucas
    Commented Nov 7, 2017 at 16:30

What you are dealing with here is a water cooled heat pump. As the head pressure builds in the cooling mode this valve allows more water through to dissipate the excess heat. If it is on the heating side, as the suction pressure drops it allows in more water providing heat to be absorbed by the system. I appears to be adjusted all the way down, someone is clearly out of their depth. This is an extremely sophisticated system requiring specialized knowledge. I would encourage you to do some home work to find someone familiar with and trained on water cooled heat pumps. You might look for the name plate find the manufacturer and call them to make recommendations as to service providers. I doubt seriously that this valve is causing the water hammer. This is not a solenoid activated valve it is a temperature activated valve. By what I see in the pictures I believe that it was likely installed in the 80's. From what I see in the pictures and the age they indicate I expect this system has given its usable life. Be careful not to put a lot of money in a system that is due to retire. With this valve adjusted all the way down as it is, it is already essentially bypassed. At this adjustment level, it is likely the compressor has been seriously compromised; very expensive repair.
Second Option: Consider starting with a clean slate.


I wouldn't bypass a solenoid without knowing what it does. Safest solution is to add a water hammer arrester to your cold water line near this thing that is causing the water hammer.

Put a container under the leaky solenoid so you can visually tell how much water is actually leaking to determine if you should have it replaced. If the leak is greater than what can evaporate naturally, then replace it.

My guess is that the solenoid is adding water to your closed loop geothermal system. If it is operating fairly often there might be a leak somewhere else and by bypassing the solenoid the system will run out of water eventually. (Or if you force it to stay open you'll have a wide open connection between the cold water line and your geothermal loop and I don't think that's any better.)

http://www.supplyhouse.com/Watts-0121227-1-2-LF150A-Water-Hammer-Arrestor-Lead-Free Watts LF150A

  • It's actually an open-loop system. Water goes from the well through the heat pump and discharges into the backyard. It was installed in the mid-1980's.
    – Lucas
    Commented Nov 3, 2017 at 20:01
  • @Lucas I had no idea that geothermal open loop well water systems were a thing. I would have thought the discharged water would be seen as a waste of resources and banned for no reason. Anyway, still I think you should either add a water hammer arrester and/or replace the solenoid. It's possible the solenoid is "bouncing" because of mineral/scale build up that you'll have more of in a open loop system since you're constantly introducing new water.
    – Dotes
    Commented Nov 3, 2017 at 20:23
  • They're not allowed anymore for the reason you stated. Lots of lakes in this area and I've heard some old systems even draw directly from the lake water and discharge back. Once our system fails, we will need to convert to standard HVAC. Too expensive to put in a closed-loop system after the fact.
    – Lucas
    Commented Nov 3, 2017 at 20:28
  • @Jeff that is not a solenoid - in the ops pictures - it is an Arrestor. After years of use it has gone bad. The op has correctly identified where his noise is coming from and the fact that the op has water hammer indicates it has failed.
    – Ken
    Commented Nov 4, 2017 at 6:51

That does not look like a solenoid to me - it actually looks like a water hammer arrestor! Since you have the hammer and you traced it back to that unit - your arrestor is BROKE..and needs to be replaced.

There are 4 screws on the top of it - that look like the point of disassembly. The Spring Compressed in that unit is a big deal - so don't touch it!! Those pipes look like 3 inch water lines - so a new arrestor will need to be sized for that.

Your service company might have been thinking you were talking to them about a solenoid - which is a completely DIFFERENT animal all together and I would think is the reason they said you should try to by pass it. Of course the device could be mounted upside down and the cover you need to find the pin on could be on the bottom side.

" The local firm that installed the Tetco unit is still in business " are they familiar with that unit as well - you might want to have them do this job for you. Just looking at the pipes (age - HINT much more stubborn to remove) and the fact that you should not touch that arrestor.

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