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Water hammer from mid position valve

Discussion in 'Plumbing and Central Heating' started by Rad1o, 16 Jan 2021.

  1. Rad1o

    Rad1o

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    In September I had to replace our CH pump. I fitted a Grundfos UPS3 15-5065 130. The pump is working o.k. When we put the CH on, we started to get a waterhammer bang which we have not had since we live in this house, which has been 21 years. But I am not 100% certain whether the waterhammer started after replacing the pump because the CH was only on occasionally then.
    The bang usually happens when the system shuts down the Central Heating. There is no bang when either CH or HW run on their own.
    I have bled the system, i.e. radiators and hot water. There was a little bit of air in the odd radiator, but no more than any time before.
    The pump is running on setting 1. I have tried the other settings too.

    The mid position valve is a Honeywell V4073A1039 which has been in the house for a long time. Nothing else apart from the CH pump has been changed or fixed recently.

    Does anyone have an idea how we can get rid of the bang easily? Or does the 3-port valve have to be replaced?
     
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  3. rbranco

    rbranco

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    Have you got a ABV?
    When the boiler stops is there pump overrun or does the pump straight away?
     
  4. Rad1o

    Rad1o

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    ABV - Automatic bypass valve? No.
    When the room thermostat clicks off there is a brief overrun and then we get the bang.
     
  5. rbranco

    rbranco

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    Sounds like your pump is still running when the valve shut, could be the valve switch is lazy and does not cut the pump quick enough before it closes.

    What boiler is it?
     
  6. Rad1o

    Rad1o

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    The boiler is an almost historic Potterton, still working, will go at some stage.
     
  7. rbranco

    rbranco

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    You may need ABV to be installed between pump/valves and return flow. Or look inside of valve and see if there is a way to tweak the microswitch so it opens before valve is completely shut.
     
  8. MeldrewsMate

    MeldrewsMate

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    Potterton Profile has pump over-run, not sure about its predecessor the Prima or even the Netaheat....but that's not important because the boiler hasn't changed.

    A simple question, did you install the new pump in the correct orientation?

    Additionally, does the 'bang' appear as a single bang, as opposed to several bangs in succession?

    This suggests that it only occurs when the HW is still on when the CH shuts off at the timer. What happens when the CH reaches temperature and the room-stat turns off the CH?
     
  9. rbranco

    rbranco

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    And ive looked over that its a 3-port valve so it never really closes, I was thinking S-plan for some reason. Whichever way there would be flow, either to HW or CH.

    Can you lock the valve position to CH then shut off the timer and see if the bang happens.

    @MeldrewsMate what if, the power loss to the valve when CH shuts down, but pump is still running might be forcing valve quickly and slam port A closed.
     
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  11. Rad1o

    Rad1o

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    The pump orientation and position is correct as per istallation instructions.
    The bang is pretty much one bang, sometimes reverberates a little.

    When only one system is in use, i.e. HW or CH and the heat call goes off, there is no bang, only when the 2 operate together.

    I went through the different operating modes that Danfoss UPS3 uses. So far I have only used the constant curves as they were the most obvious to use, but I went into the prportional speed settings late last night and there was no bang when the CH thermostate clicked off with the HW still on. I have to watch this setting again, hoping that that might solve it. I never thought to toy with pump mode settings as the old pump was pretty digital - on or off.
     
  12. Jason Odell

    Jason Odell

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    The bang is probably a worn out three way valve . When they sometimes make a bang when springing back to hot water mode when heating shuts down . That is most likely when it does it , and the flow of water through it makes the ball shut the heating port very suddenly causing a bang , if you have a bypass valve it’s not normally as bad but sounds lime worn 3 way valve
     
  13. ianmcd

    ianmcd

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    Post a pic of the pump and the valve, it does sound like the pump is the wrong way round
     
  14. rbranco

    rbranco

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    Look at the arrow on the side of the pump body, I recently replaced my pump for a UPS3 and out the box it flowed up (if you mount body with label RWU) but my flow is down towards valves so I had to take body off and turn it around so it looked all correct.
     
  15. MeldrewsMate

    MeldrewsMate

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    It does indicate that your pump may be pumping the wrong way.
    The arrow on the pump body indicates which direction it will pump regardless of which way up the writing is.
    The pump should pump towards the AB port.
    When the timer 'goes off' there is still power to the valve actuator, but it will NOT stay in the mid position.

    Try the following:
    1. Remove the actuator.
    2. Run the heating....any setting that makes the pump run will do.
    3. Using fingers or a small spanner turn the valve shaft towards its limits. Does it bang as it reaches each limit?
     
  16. Agile

    Agile

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    Check the arrow on the valve body is in the correct direction first.

    No point in looking for other problems.

    Now with CH on, if you go to the boiler and feel the temp of the pipes, is the flow pipe the hottest???
     
  17. Rad1o

    Rad1o

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    The problem was solved by changing the pump modes on the CH pump, i.e. by reducing the overrun - I think if I interpret the manual correctly. Nothing else has changed and the water hammer is gone.
     
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