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POTTERTON PERFORMA 28i hot water problem.

Discussion in 'Plumbing and Central Heating' started by Jordylee, 23 Sep 2021.

  1. Jordylee

    Jordylee

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    Can anyone help? I've got a Potterton Performa 28i with a Hot water problem. The boiler switches to DHW fine, all lights correct and no faults indicated. The boiler fires and indicated temp rises to 80 degrees but the water remains lukewarm unless you turn the flow down to a trickle - (I’d guess 1-2 litres per minute). Once 80 degrees is hit the boiler shuts off and then cycles like this until the hot tap is turned off.

    Notes. Heating works fine. There is no pass by from the Diverter Valve assembly. This was replaced in 2020 along with the actuator motor. The plate heat exchanger is new (I thought that this was the problem - but no change). New auto bleed valve on pump. I've isolated both the thermostatic shower valves in the house to ensure they're not sending cold back to the boiler. I haven't checked the thermistor yet? I was convinced it was the plate heat exchanger!

    Any advice would be greatly appreciated!
     
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  3. DP

    DP

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    System is dirty, sedimented, needs cleaning. Item that produces hot water is bunged up with system dirt
     
  4. Jordylee

    Jordylee

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    Thanks DP. You are referring to the primary heat exchanger? As well as the whole system?
    In your experience can this be sorted or improved with chemical flush etc or component cleaning/replacement?
     
  5. DP

    DP

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    Secondary HE. The one that heats the water
    That is why the radiators are fine.
    System needs cleaning whatever method you use.
    Chemical cleaning might sort the problem. Else you will need to replace the part
     
  6. picasso

    picasso

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    Change the pump head.
     
  7. DP

    DP

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    Lost me there Picasso
     
  8. picasso

    picasso

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    The op has changed the plate heat exchanger, the diverter is not passing so chances are the pump is blocked or dying and causing poor circulation of the primary water.
     
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  9. Jordylee

    Jordylee

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    Thanks Picasso. I'll look at that for sure.
     
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  11. ianmcd

    ianmcd

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    but the heating is working fine :rolleyes:
     
  12. picasso

    picasso

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    And ..... might be feck all resistance in the heating circuit against the fairly high resistance of a plate heat exchanger but I am sure you knew that.:rolleyes:
     
  13. DP

    DP

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    Surely it is the other way Picasso.

    Circulation through the PHex is almost like a S/c unless it is bunged up with muck hence primary temperature is spiking and burner cycling.

    Primaries to the rads will have inherent resistance due to pipe length, bends, fittings, rad valves and radiator resistance. Yet the heating is fine.

    Weak pump obviously would push flow temperature upwards, but this is surely found out by checking differential temperature.

    Pity boiler is not a 105e, a lot could be gleaned from observing how system components are behaving.

    If attending, I would want to take temperature readings around the boiler during HW and or CH demand
     
  14. picasso

    picasso

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    Capture.PNG The boiler is not running at full whack on heating, the pump could be on its last legs and would still heat the rads , how many people notice the heating is taking a bit longer to heat up especially on a small system, it could be something else but unless I was standing in front of the boiler its all guess work.
     
    Last edited: 25 Sep 2021
  15. DP

    DP

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    Resistance in plate heat exchanger surely will be same as resistance in resistive network in parallel connection

    A resisistor of 10 ohmes with same parallel connected will have total resistance of 5 ohmes
    More the parallel connections, less will be the effective resistance
     
  16. picasso

    picasso

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    The heating will modulate the gas rate as the temp rises , the hot water thermistor sends a value that the hot water is luke warm so the gas rate ramps up, if the pump is running slow it cant push enough water through the plate to clear the heat the main heat exchanger is making, a plate cant be compared to resisters in parallel as water does not act like electricity in this case.
     
  17. DP

    DP

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    Grant you the first one. Been there and got the tee shirt too

    Second one, why not. Asking as I want to learn.
     
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