Trap primer on hot water heater constantly flowing

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Potatohead, Jan 30, 2013.

  1. Potatohead

    Potatohead New Member

    Vancouver, BC
    I live in a four year old house. By code here, it is required to have a trap primer on any floor drain. My hot water heater (in basement) has a drain beside it which the trap primer flows into, which is fed by the cold water inlet of the hot water heater.

    For about three years now, the flow into the drain is more than what it should be. It is basically a constant slight stream, and the primer hisses to the point I can hear it on the second floor near the stairs. I never really worried much about it but my last water bill was more than normal, so I checked on it, and it definitely getting worse.

    I'm not sure if I want to replace the primer or just get rid of it. The only primer I can find around town (Watts A200) seems to be a continuous flow and not a pressure activated flow. I think this is what I have now already as it looks similar. I don't want to buy and install a continuous flow primer and have the same problem, but I can't seem to find a pressure activated one very easily. I'm thinking to remove the primer altogether and just give the T&P valve a pull every week or two, which drains to the same spot.

    Any input on which is the best route to go?

  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    The T&P valve should not be relied on as a regularly opened valve to solve the problem. Is there something else nearby (say the washing machine) that might be used to prime that trap when you run it? If the trap is not primed occasionally, it will provide an open path to the sewer. You don't want to rely on having to remember to do this.
  3. Potatohead

    Potatohead New Member

    Vancouver, BC
    Well, I do agree with you, and I have dug into this a bit more. I originally posted from work and was going off memory.

    The valve I have, is this...


    Turns out it's a thermal expansion valve, and not a trap primer. I guess I have this because my house is newer and is plumbed with pex which is only rated to 100 psi, when the t&p goes to 150. I went to HD to try and find a replacement and the guy looked at me like I had two heads.

    The thing I don't understand is why it's constantly flowing if it's rated to burst at 100 psi. I honestly don't care about the few bucks in water, but the hiss is super annoying. I took the expansion valve off the shutoff and it looks very clean inside. I CAN blow through it, I'm not sure if it should be air/water tight or not. I also turned the water pressure in the whole house way down, to the point water would barely flow through a tap, and it still allowed water through.

    At this point I am not sure if this is normal or if it should be replaced.
  4. Terry

    Terry Administrator Staff Member

    Bothell, Washington
    And that's why we install expansion tanks for water heaters. The expanded water compresses the rubber bladder inside the smaller tank, instead of draining water out.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona
    IF it is flowing "constantly" then the assumption would be that the pressure is higher than 100 psi, which would normally mean you need a pressure reducing valve, or replace a defective one if you already have one. However, if you can "blow through it" and are not blowing 100 psi, then it must be defective. Thermal expansion, which would require an expansion tank, is NOT a continual process and would only excrete a small amount of water for a fairly short time and then stop. A "true" trap primer also does not run "constantly". Some operate when a flow of water goes through them and others respond to changes in pressure, but NONE run all the time.
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