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Why has my Megaflo tank been installed with a pump on the outlet??

Discussion in 'Plumbing and Central Heating' started by jfsoar, 11 Aug 2021.

  1. jfsoar

    jfsoar

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    I've just moved into a new (to me) house. The CH and hot water setup obviously have a few issues that I was postponing diagnosing until the autumn, but the hot water programmer is now failing to call for heat, so I need to get to the bottom of what's going on sooner rather than later. The house is about 20 years old.

    Prior to the failure, we only really had HOT hot water downstairs, and upstairs only if either (a) a particular tap in the main bathroom was turned on first, or (b) if the programmer under the boiler was currently calling for heat.

    Today, spurred on by the failure (which I assume is likely to be a failed tank thermostat or zone valve since the boiler successfully fires up when the CH is turned on) I had a good look in the airing cupboard for the first time, and was surprised to see a pump on the outlet of the Megaflo. Given the Megaflo is unvented, why would it be there and what would be its purpose?

    I've added a photo elsewhere in the airing cupboard -- the pipework looks to me to be a bit over complicated. There are two zone valves and an additional pump there so assume this is a y-plan system.

    Will eventually call a plumber to remediate but would like to do as much as possible to diagnose the problem first. Any recommendations for good fault finding plumbers in Suffolk gladly received.

    hw1.png
    hw2.png
     
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  3. kidgreen61

    kidgreen61

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    Your system is piped as an S plan.
    Easy to fault find, does the HW zone valve open when HW called for?
    If not you need to find out why.
    If it does, most likely a faulty switch in the ZV actuator.

    I've never seen a pump in that position, I'd guess someone's tried to plumb in a circulating system so that there's no delay when you turn on any hot tap.
    If that's the case, you'd expect the pump on the return (usually marked secondary return on cylinder)
     
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  4. JohnD

    JohnD

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    Note the pump is painted yellow. This is the bronze circulating pump, for sending hot water round the hot pipes so there is not a lag when you turn on a distant tap. Very expensive but I believe they now make a stainless one that is a bit cheaper.

    If you ever sell it, try to get a good price.

    I once had one but in my current house I just put up with the delay.

    rather wasteful in energy as the hot water pipe will act like a long thin radiator. I don't know if it's possible to have a timer or an occupation switch so it only comes on when needed. I think it will obstruct flow when it is turned off.
     
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  5. ianmcd

    ianmcd

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    As @JohnD correctly says it is a secondary return pump, it is bronze and it circulates the water that comes out of the taps to ensure you get HW a lot faster, this pump will have no bearing on the boiler firing when the HW is selected, select HW on at the programmer and see if the HW zone valve opens, the small lever at the top should prove some resistance when switched off, when you try to slide it across to man, when selected to on, there should be no reistance if working correctly
     
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  6. jfsoar

    jfsoar

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    Thanks very much all. That makes sense. The hot water zone valve is not operating when hot water is selected, and provides equal resistance whether HW is on or off. Will put a meter on it to see if it is getting power.

    The recirculating pump makes sense, and might help me diagnose some of the other problems (lukewarm water at some taps, warm water thru the cold tap). Will see if it is on all the time -- it appears to be. It looks like the hot water then recirculates back into the inlet side of the tank. I expect this is acting (as you say) like a long radiator, running next to cold pipes thru a bunch of loft insulation. Will aim to put it on a timer for morning/evening if it doesn't restrict flow too badly.
     
    Last edited: 11 Aug 2021
  7. JohnD

    JohnD

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    I can't see all the pipework, but is there a valve to bypass the yellow pump?
     
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  8. picasso

    picasso

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    The pump is in the wrong place.....

    Capture.PNG
     
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  10. JohnD

    JohnD

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    good point

    if it was on the return, then it would not impede flow of hot water to the taps when turned off, right?

    so if you felt like it, you could use a timer or occupancy switch in the distant bathroom

    In my previous house I closed off the circulation because I felt it was not worth having, and cooled the cylinder.
     
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  11. I always put mine on timers... Grundfos do a pump that learns your patterns so turns on just before there is a demand. The bronze pump should either be on the side ¾ of the way up or on the cold inlet at the bottom of the cylinder.
     
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  12. The problem you would get with doing that is stagnation. I always try to fit them as if they are done well they work a treat. They are fitted also to prevent from Legionnaires. Hence why hospitals and care homes have them.
     
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  13. aptsys

    aptsys

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    Yes, the secondary pump realistically can be extremely low flow when installed in the correct place since it only needs to replenish water at a rate that maintains sufficient temperature to each tap. It will be restricting flow where it is currently sited.
     
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  14. This will be heat transfer. Cold pipe touching the hot pipe or worse the heating pipes
     
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  15. jfsoar

    jfsoar

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    Thanks very much all, I replaced the powerhead on the hot water zone valve and it's all back up and running. Replaced the old Honeywell programmer with a Nest while I was at it (no thermostat before) and all appears to be working OK. Will judge the lukewarm water more in the winter.
     
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