2 pumps on 1 hot water tank

Discussion in 'Plumbers' Talk' started by GordonK, Nov 12, 2017.

  1. In theory, the pump choices are sensible.

    Could you provide an exact model number for the lower pump, please? If it's pressure-operated, then I think that could explain its behaviour. If 'flow', then it doesn't make sense to me.

    Anyhoo - can you answer, please - does the lower pump CONTINUE to run for as long as the upper one is running?

    I'd also suggest that a good step to take would be to contact ST themselves, and give them a summary of the info as you've given us, complete with diagram.
    GordonK likes this.
  2. If the lower one has a flow switch, what 'flow' is causing it to come on?

    Do pumps have either a flow or pressure-operated switch? If the lower one is 'pressure', then that - I think - could explain what's going on.
    GordonK likes this.
  3. Dr Bodgit

    Dr Bodgit Well-Known Member

    Good point DA, I was wondering that myself. ST pumps work on flow detection via a reed switch (AFAIK), I have bought one and looked into it. Now, I can see that the lower pump might get turned on by a lowering of water pressure, albeit slight, but it would soon turn off as the water at now higher pressure has no where to go. Then it would cycle on/off if anything and not stay on permanently.

    I certainly concur with your recommendation for the OP to contact ST customer services for advice.
    GordonK and Deleted member 33931 like this.
  4. GordonK

    GordonK Member

  5. That 'lower' pump looks as tho' it's 'flow' operated, and requires a min of 0.8lpm for it to switch on. So how it coming on here defeats me. But ST will have an answer :).

    There must be something weird that has the teeny-tiny 'back' flow/wobble caused by the reduced pressure from the other pump making the flow switch respond. But darned if I can work out what...

    Keep us posted - I bet there's a simple solution.
    GordonK likes this.
  6. GordonK

    GordonK Member

    Ok ... all sussed out and seems it’s working as it should.

    I had thought the lower pump stayed on when other pump was in use , turns out this wasn’t the case entirely. It was initially so I can only assume there may have been some air trapped somewhere..

    The lower pump detects the flow release to the upper pump (maybe it pushes back initially as it comes on) and kicks in for 2 secs then goes off .. so not running all the time.

    The upper pump doesn’t do a thing when the lower pump comes on ...

    So it seems ok but glad I’ve asked the question as it seemed odd ..
  7. Dr Bodgit

    Dr Bodgit Well-Known Member

    Just live with it then, reasonable outcome.
    GordonK likes this.
  8. Cool - thanks for being brave enough to come back with that :p

    Yes, it must be that the 'pulse' of the other pump firing up is enough to draw a slug of water over the other pump's flow switch - possibly even from the copper pipe flexing slightly under the pressure drop.

    Good result - that actually sounds pretty normal :)
    GordonK likes this.

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