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Should pump overrun happen every time boiler switches off (Potterton Profile 80e)?

Discussion in 'Plumbing and Central Heating' started by Spiderpig, 18 Oct 2019.

  1. Spiderpig

    Spiderpig

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    Hello, Should the pump overrun every time demand switches off (or is it a safety feature as-and-when)? My pump is not overrunning at all but the boiler is working ok but only when set to low, max 2 out of 5. Above setting 2 sometimes the overheat switch trips. I suppose if the overrun was working then I should be able to set boiler to a higher setting?
    Thanks!
     
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  3. ianmcd

    ianmcd

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    in order for the pump overrun to work you will need a permanent live and a switched live, make sure it is wired correctly
     
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  4. Harry Bloomfield

    Harry Bloomfield

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    Modern boilers have an output which is able to directly control the pump, to allow them to over run after the boiler has shut down. Idea is to remove the residual heat in the boiler's water jacket. That helps to both protect the water jacket and help a little with efficiency. As you are finding, the residual heat can trip the over heat stat. Wired properly, that should not trip.
     
  5. Spiderpig

    Spiderpig

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    Thanks for the replies. Does the boiler *always* overrun the pump whenever it stops heating or is it only rarely that it should be necessary? I am trying to work out whether the overrun is completely broken and never works. Is there a way I can force the boiler to try to overrun or should that already have happened any time the temp is high enough to trip the over heat stat, regardless of any other fault there may be (blockage/poor flow or something)?
     
  6. Harry Bloomfield

    Harry Bloomfield

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    The pump should always over run for several minutes irrespective. It could be that an older boiler which didn't support over run, was replaced by a more modern one - in which case there may have been no separate wire from the boiler to the pump, to enable the boiler to control the pump.

    The old way was for the pump to only run, when there was a call for heat to the boiler. Boilers back then had heavy cast iron water jackets. Modern boilers are much lighter and use much thinner water jackets, so pump over run is essential.
     
  7. Spiderpig

    Spiderpig

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    That's great, thanks for confirming. I'll do some investigation on the wiring to the pump...
     
  8. ianmcd

    ianmcd

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    your boiler can be installed fully pumped or pumped CH Gravity HW do you know which system you have ? if you dont post some pics of your boiler showing the pipes leaving it above and below
     
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  9. endaxi

    endaxi

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    For about 13 years (since our house was built) we had a Potterton Heat-Only boiler and a pump in the airing cupboard. It was a very problematic boiler so two years ago we decided to get a new one. It was only when I got some quotes that I was informed that we should now have a pump over-run and we didn't then have one.

    When the new boiler was installed we had to have a new cable run from the boiler to the airing cupboard to enable a pump over-run.

    I remember trying it out and found that even if the boiler is switched on for a few seconds the pump would over-run for a few minutes when it was switched off.

    Hope this helps.
     
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  11. endaxi

    endaxi

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    Just a thought... If you don't currently have a pump over-run facility then it's worth checking (or getting checked) if you have some redundant wires in the cable that currently runs from your boiler to the airing cupboard (assuming your pump is in the airing cupboard). This would make it an easy job to get the over-run enabled. We had no spare wires so had to have a conduit fitted on an outside wall to take the new cable between the two locations.
     
  12. Mottie

    Mottie

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    My old Potterton profile 60e that I had for around 25 years with a Y plan setup would overrun only when it was very hot. If it wasn’t very hot it would stop as soon as a heating demand (either hot water or heating) was switched off. Like you, I could never run it at maximum output, even from new, without the overheat button popping. I think it was something like 80% of maximum power but not as low as yours. My new Vaillant runs on for exactly 5 minutes every time the heating/hot water stops. Even if I put the heating on for a couple of minutes and then switch it off, it will run on for 5 minutes.
     
  13. Harry Bloomfield

    Harry Bloomfield

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    I also lacked a spare cable for my pump over-run. Boiler on kitchen wall, other end of kitchen from airing cupboard/pump. I managed to hide cable up to ceiling above boiler, then push the cable through hidden behind gap behind coving, then up through ceiling, into airing cupboard.
     
  14. ianmcd

    ianmcd

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    Some boilers the pump over run is temp controlled and will run when the boiler decides, some are time controlled and will run for a set time every time the boiler has fired
     
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  15. endaxi

    endaxi

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    Thanks for that info. Looks like I have the latter.... Worcester Bosch Greenstar 24Ri. Just tried again out of curiosity... fired boiler for 10 seconds and pump over-ran for about 3 minutes.
     
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  16. dilalio

    dilalio

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    Think of all that wasted leccie :eek::whistle::sneaky:
     
  17. JohnD

    JohnD

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    let me see...

    34 Watt pump runs for 30 hours on 15p worth of electricity

    That's half a penny per hour.

    So 3 minutes is, um....

    too little to worry about.
     
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