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  1. chappy2000
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    chappy2000 EF Member

    Location:
    london
    Hi, hoping someone can help me out. As part of a rewire I'm connecting up an unvented system and separate boiler for the heating. Boiler, pump and stat for heating all working but I have no experience of unvented cylinders.
    I basically have the cylinder, 2 port valve and pump. Looking for a basic understanding and help with terminals. I have 6 terminals on the cylinder ( currently wired with a perm l from a timer switch. The other 3 terminals go to a separate device, thermostat / cut out?
    I will attach a picture if possible. Thanks in advance.

    20170728_164206.jpg

    20170728_164145.jpg

    20170728_164151.jpg
     
  2. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    3 terminals are the immersion and the other are for the cylinder stat
    You'll need 3 connections for a y plan at the cylinder or if it's an s plan then just 2
     
    Last edited: Aug 3, 2017
  3. davesparks
    Online

    davesparks Trusted Advisor

    Location:
    guildford
    The three unused terminals are the C NC and NO connections of the cylinder thermostat. The overheat cutout is usually built in to the thermostata unit in this type of cylinder, but check the manual to confirm.

    Connect it as per usual for a hot water cylinder if it is S plan, if it is Y plan the you need to add the two port valve in to the standard circuit so that the DHW demand from the cylinder stat opens the 2 port valve and then the microswitch of that valve fires the boiler.

    What is that pump for, It looks like a secondary circulation pump?
     
  4. Leesparkykent
    Online

    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    As Dave says the yellow pump looks like secondary hot water return and will have either bronze or stainless steel internal components. Usually with a secondary hot water return I put the pump on its own single channel programmer so the customer can time it to come on before they are most likely to be using the hot water.
     
  5. buzzlightyear
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    buzzlightyear Electrician's Arms

    Location:
    star command
  6. chappy2000
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    chappy2000 EF Member

    Location:
    london
    Hi, thanks for the quick reply.

    It's a direct system and the manual was not very descriptive at all, no schematic only a diagram showing 1,2,3 from the valve. Yes I think it's a circulation pump due to the side of the property in guessing.
    It's currently temp connected by the plumber so the pump runs continuously and it just have a perm feed on timer. I was hoping the system would come pre wired ready for me to just add a timer & feed.
     
  7. buzzlightyear
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    buzzlightyear Electrician's Arms

    Location:
    star command
    which company is the cylinder from.
     
  8. sam400
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    sam400 Regular EF Member

    Location:
    sussex
    Hi you normally have the overheat stat and the standard stat in series as an extra safety precaution. Usually the link is pre wired so timer goes on one stat and valve on the the other.
     
  9. sam400
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    sam400 Regular EF Member

    Location:
    sussex
    Sorry ignore my post, just had a closer look at stats looks like they have 2 stats in the one unit.
     
  10. davesparks
    Online

    davesparks Trusted Advisor

    Location:
    guildford
    It is not a direct system, it is an indirect system.
    A direct system is one where the domestic hot water is heated directly by a source of heat, for example by an immersion heater.
    An indirect system is one where the domestic hot water is not directly heated by a source of heat, for example a boiler heats water which is then circulated through a heat exchanger to heat the domestic hot water.

    Don't guess with an unvented cylinder, the controls need to be correct as they incorporate a safety system intended to prevent overheating and possible explosion of the cylinder.
     
  11. davesparks
    Online

    davesparks Trusted Advisor

    Location:
    guildford
    It looks like a mega-flo unit which is made by Heatrae Sadia
     
  12. chappy2000
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    chappy2000 EF Member

    Location:
    london
    Hi, this system is not connected to the boiler, it's stand alone hot water, does that not make it a direct system as the water is heated directly by the source ( element).
     
    • Like Like x 1
  13. Lee42
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    Lee42 Lee

    Location:
    England
    Sounds like you need to get someone in who knows what they are doing.

    Why is there a two port valve on the system if it's not connected via a boiler?
     
  14. chappy2000
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    chappy2000 EF Member

    Location:
    london
    Every unvented has a 2 port, fail safe / safety device
     
  15. Lee42
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    Lee42 Lee

    Location:
    England
    I thought that was only when connected via a boiler?
    You mentioned it is only heated via a immersion which will have its own safety cutout
     
  16. Leesparkykent
    Online

    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    Lol if it's not connected to a boiler then why have a two port valve? The Plumber can't have his G3 ticket as he has the very basic principals of how the system works wrong.
     
    • Agree Agree x 1
  17. Taylortwocities
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    Taylortwocities Electrician's Arms

    Location:
    Oxfordshire
    So, its a direct system with the ONLY source for heating the vessel is from the immersion???

    Not just normally, this is an absolute requirement. The overheat cylinder control MUST be wired in series with the heat source (the immersion).
    They are the things that stop the vessel boiling and squirting super-heated water over everybody should the immersion's temperature controls fail.

    Installation of unvented heated water vessels is notifiable to the local authority and you need a G3 qualification to do it.
    EDIT:
    Extract from guidance
    The Local Authority Building Control must be notified of the installation of an unvented hot water storage system as they are subject to the legal requirements of Building Regulation G3. The system must be installed by a ‘competent person’ who holds the relevant qualification for the installation of unvented hot water cylinders. The installer must be able to provide a card issued by a body such as the Institute of Plumbing (IoP) or the Construction Industry Training Board (CITB).
     
  18. Taylortwocities
    Offline

    Taylortwocities Electrician's Arms

    Location:
    Oxfordshire
    So, its a direct system with the ONLY source for heating the vessel is from the immersion???

    Not just normally, this is an absolute requirement. The overheat cylinder control MUST be wired in series with the heat source (the immersion).
    They are the things that stop the vessel boiling and squirting super-heated water over everybody should the immersion's temperature controls fail.

    Installation of unvented heated water vessels is notifiable to the local authority and you need a G3 qualification to do it.
    EDIT:
    Extract from guidance
    The Local Authority Building Control must be notified of the installation of an unvented hot water storage system as they are subject to the legal requirements of Building Regulation G3. The system must be installed by a ‘competent person’ who holds the relevant qualification for the installation of unvented hot water cylinders. The installer must be able to provide a card issued by a body such as the Institute of Plumbing (IoP) or the Construction Industry Training Board (CITB).
     
  19. andyb
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    andyb Electrician's Arms

    Location:
    West Sussex
    Looking at the 2nd picture it would seem that it's plumbed as indirect. The valve is on the flow. You need to wire the tank stat to controll the valve. The immersion will just be a back up and not the primary heating source.
     
    • Agree Agree x 1
  20. buzzlightyear
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    buzzlightyear Electrician's Arms

    Location:
    star command
    Last edited: Aug 4, 2017
  21. davesparks
    Online

    davesparks Trusted Advisor

    Location:
    guildford
    If it's not connected to the boiler then why does it have a flow and return pipe connected to it, and a two port valve?

    That is an indirect cylinder, not a direct one.
     
  22. davesparks
    Online

    davesparks Trusted Advisor

    Location:
    guildford
    Only indirect cylinders do. There is nothing for a valve to operate on in a direct system.

    The safety cutout on a direct system is incorporated in the immersion heater thermostat.
     
  23. Sparkgap
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    Sparkgap EF Member

    Location:
    Somerset
    All unvented cylinders have mechanically operated temperature/pressure relief valves. I have also seen more recently cylinders with two-port motorised valves on the hot water outlet with an over temp thermostat which shuts it if the water gets too hot. This is because even if the overtemp cutout on the immersion heater works you still have a cylinder full of too-hot water.
     
  24. anthonybragg
    Online

    anthonybragg Electrician's Arms

    Location:
    NORTHAMPTON
    Business Name:
    CHARLTEC ELECTRICAL LTD
    Reading this post has not answered the OP question.
    These unvented cylinders should have immersion heaters with H/L stat built in.
    How is the domestic hot water being heated the impression I get is direct from the immersion heater in which case as Davesparks posted the pump is secondary hot water pump via time clock which makes sense. What is the valve for ?.
     
  25. davesparks
    Online

    davesparks Trusted Advisor

    Location:
    guildford
    That is an indirect cylinder, the motorised valve is on the flow connection.
    The yellow pump is a secondary pump,
     
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