Tankless heater turns on when irrigation system shuts off

Discussion in 'Irrigation / Sprinkler Forum' started by Mike zsohar, Jan 19, 2020.

  1. Mike zsohar

    Mike zsohar New Member

    Joined:
    Jan 19, 2020
    Location:
    Tampa Florida
    When one of my irrigation zones shuts off my tankless water heater turns on for a second or two.
    The display shows about 0.7 gpm briefly and goes to zero.
    Increased pressure is seen at the sink faucets during these events.
    This sometimes happens when a zone turns on but every time when they shut off.
     
  2. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    Did this always happen or just started, or after the tankless was installed? Are you on a well or city water? Sounds like a water hammer effect and on the recoil the pressure drops just enough to activate the tankless. If you are outside when a zone shuts down you hear a thump? Is it any zone when it shuts down? If you are on city water and the irrigation system was installed when the home was built, it had to pass inspection with a anti backflow or anti siphon device. Do you have a indexing valve for the zones or individual valves for each zone? With an indexing valve when the timer shuts off the solenoid so the it can rotate to the next zone, you may see all sprinklers momentarily squirt water. That can drop the pressure for a second or two.

    Not sure what the fix can be but it will depend on the cause. You can put a pressure gauge on a spigot that is before the irrigation system and look at the needle as a zone shuts off. You might be able to get an idea on the pressure drop. Is there an adjustment on the tankless? Some irrigation systems may have a shut off valve before the backflow preventer. Close it down to reduce the water flow to the irrigation system. When a zone shuts down it should reduce a hammer effect if it is the cause. Then install a hammer arrestor. This one (the HD link) can be threaded in a spigot and get a cap of the other end before cutting into the system whereby the arrestor doesn't take care of the problem.

    With the pressure gauge it will give you what your normal static pressure is and when the water flows to the irrigation system. If the pressure is over 60 PSI while the water is flowing, a pressure reducing valve maybe needed.

    https://www.homedepot.com/p/The-Plu...estor-for-Washing-Machine-HA34WM-NL/308601314

    https://www.homedepot.com/p/Watts-3-4-in-Plastic-Water-Pressure-Test-Gauge-DP-IWTG/100175467
     
    Last edited: Jan 19, 2020
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  4. Mike zsohar

    Mike zsohar New Member

    Joined:
    Jan 19, 2020
    Location:
    Tampa Florida
    See my responses below
    Did this always happen or just started, or after the tankless was installed?
    --Unsure if it happened before tankless was installed (in Sept 2019).
    Are you on a well or city water?
    --On city water
    Sounds like a water hammer effect and on the recoil the pressure drops just enough to activate the tankless. If you are outside when a zone shuts down you hear a thump?
    --I do hear a thump
    Is it any zone when it shuts down?
    --any of the 5 zones causes it
    If you are on city water and the irrigation system was installed when the home was built, it had to pass inspection with a anti backflow or anti siphon device.
    --there is a Richdel 709PR (Irritrol) 1" shut off valve with anti-siphon installed now
    Do you have a indexing valve for the zones or individual valves for each zone? With an indexing valve when the timer shuts off the solenoid so the it can rotate to the next zone, you may see all sprinklers momentarily squirt water. That can drop the pressure for a second or two.
    --individual solenoid per zone

    Not sure what the fix can be but it will depend on the cause. You can put a pressure gauge on a spigot that is before the irrigation system and look at the needle as a zone shuts off. You might be able to get an idea on the pressure drop.
    Is there an adjustment on the tankless?
    -- no adjustment on the tankless
    Some irrigation systems may have a shut off valve before the backflow preventer. Close it down to reduce the water flow to the irrigation system. When a zone shuts down it should reduce a hammer effect if it is the cause.
    -- I did reduce the flow to less than 1/2 normal flow but issue still happened
    Then install a hammer arrestor. This one (the HD link) can be threaded in a spigot and get a cap of the other end before cutting into the system whereby the arrestor doesn't take care of the problem.

    With the pressure gauge it will give you what your normal static pressure is and when the water flows to the irrigation system. If the pressure is over 60 PSI while the water is flowing, a pressure reducing valve maybe needed.

    https://www.homedepot.com/p/The-Plu...estor-for-Washing-Machine-HA34WM-NL/308601314

    https://www.homedepot.com/p/Watts-3-4-in-Plastic-Water-
     
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