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Indirect Unvented cylinder, Combi Boiler and Nest Thermostat

Discussion in 'Plumbing and Central Heating' started by chris101, 23 Apr 2018.

  1. chris101

    chris101

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    We have just had an indirect unvented cylinder (250l Vertical Telford Tempest) installed along with a nest v3 thermostat.
    The plumber was able to modify our existing combi boiler, so it runs like a system boiler.

    I am trying to understand how it works as currently the plumber has set it to come on for 2 hours each day (1hour between 5am-6am and 5pm-6pm).
    During these times, the boiler remains continuously on and only switches off after the hour mark.
    Is this right?
    I would have thought during the set times that the boiler should come on, it would work in connection with the cylinders thermostat so once the waters heat got to a set level, the boiler will shut off.

    The cylinders booklet states it takes 28min for it to heat up.

    Could someone please advise on how this setup should be working and if there is anything I could do to make it more efficient, then it currently is?

    Thank you
     
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  3. muggles

    muggles

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    The cylinder will only take 28 minutes to heat up if the correct amount of power is being applied. What boiler do you have? Does the boiler go off if you turn the cylinder thermostat down?
     
  4. chris101

    chris101

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    Thanks for the response.
    The boiler is a Potterton Titanium 33kW. Have not tried it on a lower temp on the cylinder although will try it tomorrow and report back.
     
  5. muggles

    muggles

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    I'm interested in whether it has been wired correctly. If you have your hot water only on (no heating) and turn the cylinder stat down when the boiler has fired up, the boiler should go off again. If it doesn't, the wiring is wrong
     
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  7. dilalio

    dilalio

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    If the boiler is constantly running during this time and the cylinder is satisfied, then the surplus heat is going elsewhere... check CH pipes or rads around any motorised valves. If these are not hot then the boilers output is still going to the cylinder or a bypass.
    By reducing the cylinder stat setting you will be telling the system that it is satisfied and you should see the boiler shut off.
     
  8. chris101

    chris101

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    So tested it this morning. So the boiler comes on when it is heating up the cylinder (both gas light and rad light on boiler is lit) however it seems once it gets to the set temp, the gas light goes off but the rad light stays lit for the full duration of the set time.
    Is this normal/to be expected?
     
  9. dilalio

    dilalio

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    But the boiler does stop firing yes?
    The “rad” light as you put it may be staying on to show that a heating schedule is active but the demand has been satisfied (by the cylinder stat) and the boiler will only fire again to recover DHW temp in the cylinder if any is drawn off during th active heating schedule... water drawn after that point will not be regenerated until the next heating schedule becomes active.

    That’s how it’s normally implemented.
    Is it hot water priority and set up to interrupt CH.

    Edit: Or the boiler is reaching temp and shutting down.
    Sounds like wiring but you need see if the boiler continues to cycle with no water drawn during the demand period.
     
  10. chris101

    chris101

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    So the gas light goes off (stops firing) however there rad light stays on and there is still some noise in the boiler for the duration of the scheduled time.
    I am not sure if it is setup up as hot water priority. How can I check?

    I also noticed that it takes 40seconds for any given tap in the house to obtain hot water? Is this normal?
    The pipe work to all taps is no more than 6meters and from the cylinder they are connected with 22mm plastic pipes and copper 15mm right towards the ends where they connect to the bath/shower or tap.
     
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