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Discuss Pumps on the return in the Central Heating Forum area at

  1. billybongo

    billybongo New Member

    Can anyone tell me why it was prefered to put circulating pumps on the return side of heating systems a few years back , its just that i have circulating problems on a largeish system and i am thinking that the pump has to work so much harder , or does it because if a pump is at a neutral point wont it work well either way ? thanks for any input .:)
  2. stevetheplumber

    stevetheplumber Plumber GSR

    pump can go any way realy its the relationship between pump, cold feed and vent thats important to prevent pump over or air being sucked in years ago when we always put the cold feed and vent to seperate tappings on the boiler pump was often on the flow but i think the lower return temps prolonged pump life
    even now im comming across smc pumps that have been in 40 plus years often wonder where the worlds oldest working central heating pump is
  3. billybongo

    billybongo New Member

    Thanks steve , cleared slightly muddy water , as you say there must be a pump out there as old as the hills, never thought of cooler return temps prolonging life but obvious really .
  4. migoplumber

    migoplumber Guest

    steve's right about the prolonged pump life. with todays better component manufacture, its not so important, the news pumps are built better

    also with our newer systems generally there are 2 c/h circuits one for constant temperature, one for variable temperature. pumps need to be installed on flow for this type to system to work effieciently

  5. billybongo

    billybongo New Member

    Shaun, out of interest what is a constant temp circut , is it if say you set room stat to 20 degrees centigrade thats where it stays where as say a compensator goes with temp change outside , cheers
  6. migoplumber

    migoplumber Guest

    constant temp circuits is the boiler flow temp circuit, typically for radiators.
    variable temp cct is where a lower temperature than boiler flow is needed for example
    boiler set at 80 degreees, constant temp to hot water cylinder, and radiators, (which in turn are self regulating (t.r.v.s and cylinder stat))
    underfloor heating on variable temperature maybe 55 (controlled by a 3 way motorized valve that sends boiler flow directly back to the return when the water in the cct has reached the temperature set point) or maybe in a schooll where they only want 40 degrees in the rad.
    the boiler is designed to operate at max effiecency at a certain temp, be it 60 or 90
    using this vt cct you can obtain a desired temperatue in a designed zone, at 100% boiler effiecency

    not very good at explaining stuff, but i hope you get the jist.
  7. billybongo

    billybongo New Member

    ;)Thanks shaun, yes i do get the jist , its my language
  8. james.ball5@bti

    [email protected] Guest

  9. desalman

    desalman Guest

    I realise that this thread is, on the whole, some 4 years old but I have a question :- I have a piping schematic for a Rayburn solid fuel CH Cooker. It shows the pump on the return but before the injector tee. Can the pump be fitted on the flow side instead? I don't imagine it would affect the injector tee as the flow into the tee would still be at pressure. Additionally, although the diagram shows the ''venturi suction'' inlet to the tee from the cylinder return + the feed & expansion tank is there any reason why that inlet could not be just from the F & E tank with the cylinder circuit being treated as another radiator.
  10. AWheating

    AWheating Trusted Plumber GSR

    with standard solid fuel installs the cylinder cant be treated as another radiator, it needs to be gravity and open to stop major safety issues. Best to employ a hetas qualified engineer to install it for you.
  11. tamz

    tamz Guest

    Follow the Rayburn instructions. It will save a lot of explaining as why it should be like that and get someone who is qualified and knows what they are doing to fit it.
    • Like Like x 1
  12. Dotty

    Dotty Guest

    Definitely not a diy job. You may not believe it but the majority of your plumbing will try to kill you if you give it half a chance.

    As AW and Tamz have rightly stated, get a HETAS qualified guy (or gal, we're all for equality!) in.
    • Like Like x 1
  13. desalman

    desalman Guest

    I may have given the wrong impression, I have no intention of doing a DIY install.

    The primary question was regarding the position of the pump - on flow or on return, does it make a difference ?

    Regarding the DHW cylinder, I am in France, conventional DHW cylinders are not open vented but have an over-pressure protection via a 'group de securite' or a pressure relief valve discharging to outside.

    I appreciate the need for a gravity system and permanent 'heat leak' in case of pump power failure / all TRVs closed. The cylinder feed would / will not be capable of being automatically valved off, neither will the bathroom radiator. It is anticipated that all other rads will be fitted with TRVs.

    HETAS is, I believe, a UK qualification but I will, in any case, be contacting an ex-UK HETAS installer who now has a business in my part of France
  14. AWheating

    AWheating Trusted Plumber GSR

    maybe it would help to mention the fact your in france before hand :)

    in the uk you can not fit an unvented cylinder to a solid fuel source. The reason is that the unvented regulations require you to have full control of the heat source with shut off under fault conditions, you can not shut down a solid fuel appliance like you can a gas/oil/lpg appliance. Overheated unvented cylinder can take a house down if they go badly wrong.

    i would seek advise from a local engineer who understands the rules and reguations in france, im unsure if there is a franceplumbersforum??

    good luck.
    Last edited: Mar 3, 2013
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