Adding a circulating pump to boost CH

Discussion in 'Plumbers' Talk' started by Barron, Mar 6, 2016.

  1. Barron

    Barron New Member

    Hi,
    We have a very long house and the rads aren't getting hot quick enough both down and upstairs at the farthest end. Boiler is a Grant Vortex Pro Utility system installed Sept 2010. We have a Gledhill 210lt mains pressure - unvented DHW cylinder. there will be 18 rad eventually. The boiler is situated approx. 16 metre from the last rads. (Welsh long house with Extensions)

    OH though not a qualified plumber has been in the building trade all his !!!! number of years and has fitted all the CH systems in all our properties. First time we have had any problems with rads not getting hot enough - but then first time we have had a property that is so 'long'.

    Advice on which pump would suit best - thinking to put it half way between the boiler and the last rads.

    Any help gratefully received.
     
  2. chippie244

    chippie244 Super Member

    Could be talking utter tosh but I worked on a massive house a few years ago where the hot water was pumped in a continuous loop around the house and then timers and valves just pulled it off when needed.
     
  3. Ryluer

    Ryluer Well-Known Member

    Shifting the pump closer to the rads will make no difference.
    It might just be a balancing issue or pump on the wrong speed setting.
     
  4. Barron

    Barron New Member

    Hi,
    The pump on the boiler is already set at it's highest speed setting. he has tried all the normal things balancing the rads etc. He has turned off some of the rads upstairs and it still won't pump round the loop. He has vented the system but still not going right round, he thought it was air but still no joy. It's 22mm going from boiler to upstairs then converts to 15mm for rest of the loop and there are spurs coming off the loop.
    ???
     
  5. I obviously don't know if it's down to the 16m distance or having part of the loop in 15mm, or a mix of both.

    But, in theory at least, if the problem is down to friction reducing flow, then a second pump should help.

    All theory. Ideally, your mate should contact the boiler's manufacturer for guidance before trying anything.

    Things to think about - how to control that pump? Before he wires it in parallel with the existing pump, he'll need to consider things like is the existing pump an automatic variable-speed type? If so, will the PCB cope with having an extra pump connected to this?

    Also, how will he make this second pump run only with the CH and not the DHW - 'cos the boiler's pump will run with DHW too?

    A possible solution is to fit a pipe 'stat on the CH flow pipe a few inches out of the boiler so it'll switch on this second pump when it detects hot CH water. This will have the advantage of it being isolated electrically from the boiler's control circuitry. However, will having this second pump still running on 'over-run' after the boiler has been told to turn off cause any issues with the boiler internals? (Probably not - but I don't actually know...)

    If this were me, I think I'd buy a good quality automatic-speed control CH pump, possibly a little used 2nd-hand one, and install it towards the end of his system where the problem is occurring, and for a trial just control it manually - wired to a mains plug. If it's shown to sort the problem, then wire it up to a pipe stat or whatever other system he proposes.

    However, make sure the power to it is coming from the SAME single boiler isolator switch.
     
  6. Ryluer

    Ryluer Well-Known Member


    If 16m off 15mm then that's your problem. Needs re-piped and pipes sized correctly.
     
  7. kiaora

    kiaora Guest

    hi
    i agree with ryluer, often no though or knowledge, is used when installing a heating circuit.
    the friction loss can be loads, also, we call them pumps, but they are not pumps in my view, more circulators,

    one of my rules of thumb, no more that 4kw on 15mm, must me 22mm if over 4kw of rads


    regards
    peter
     
  8. Agree with you both.

    However, assuming t'Barron just can't face the cost and disruption of replumbing, then the idea of an additional circulator (I'm learning...) ain't completely mad.

    Ok, I don't expect any trained plumber - or the manufacturer of the boiler - to say "Give it a shot...", but that is not to say it isn't a potentially valid idea.

    Water flowing through a pipe can be compared in many ways to leccy flowing in a wire. If the wire's resistance is significantly reducing the flow to an unacceptable level, then the only way around this - other than replacing the wire for a thicker one - is to boost the pressure (voltage) or in this case by adding a further pum...er circulator.

    The situation is helped in this case by it being a sealed, pressurised system, so no risk of causing weird pressure issues like the drawing in of air via vent pipes or discharging glugs through the expansion pipes.

    Absolutely, I wouldn't expect a pro plumber to go round to Barron's house and suggest this - there is only one 'proper' solution.

    But that is not to say that his idea doesn't possibly have mileage.
     
  9. sam spade

    sam spade Active Member

    Is that 16m as the crow flies or the length of the pipe run?

    In either case it shouldn't be significant. The furthest rad on my system is 30m (pipe length) from the boiler. I suspect the system has been reduced from 22mm to 15mm to early. However it all depends on the design DeltaT of the system. (That's the difference between flow and return temperatures at full output.) This also need taking into consideration when selecting radiators as the output of a rad reduces if the deltaT increases.
     
  10. Ryluer

    Ryluer Well-Known Member

    If the 15mm is loaded with more than 4kw worth of rads then I think its significant.
     
  11. sam spade

    sam spade Active Member

    That may be true for a 10C differential; but if the system is designed for a 20C differential, then a 15mm pipe can carry 8kW. This is because the flow is halved and so is the friction in the pipes.
     
  12. Barron

    Barron New Member

    Hi Guys,
    Thanks for all your replies and info, just so you know 'I no nofing'.

    I am going to check the rad sizes to see how many Kw they add up to. And I am just relaying my OH's words/ thoughts etc. He becomes a 'grumpy old man' when things go wrong and he can't solve them, so if I have got things wrong and confused you all then I apologise.

    The house length is roughly made up of 4m length x 4m width (new extension) 4m L x4m w (old house- boiler situated) 12m L x 4m W (old house) and a 4m W x 8m L (new Kitchen extension goes off Old house-boiler section as a leg /spur). So sort of an 'L' shape. Total 'length' is 20m with an 8m leg.

    'However, assuming 'Barron' just can't face the cost and disruption of re-plumbing' - Devils Advocate - you are correct we have been renovating this house for the last 5 years..!!! and are now on the last bit, so to go back to reinstalling the 15mm with 22mm is not really an option. (For me.....)

    I am going to check the rad sizes to see how many Kw they add up to.

    Sam Spade - it's actually 12 metres to the farthest rad and Yes as the crow flies.

    I think OH will go with the suggestion of the circulating pump option to see if it helps. (I chose to type pumps as it was quicker than circulating). But thanks for correcting me Ryluer.
     
  13. Ryluer

    Ryluer Well-Known Member

    That was kiaora
     
  14. Ryluer

    Ryluer Well-Known Member

    Is the 16m pipe run definitely 15mm?

    How many rads on this?
     
  15. Barron

    Barron New Member

    OOoophs sorry......!!!
     
  16. Barron

    Barron New Member

    OH has for the CH 22mm from the boiler ( 7') to the upstairs then yes it's all 15mm - it's what he has always used in our other properties he has built and has never had this problem before. As I previously stated this is the first 'LONG' property - the others have been more traditional shape (squarer)
     
  17. Ryluer

    Ryluer Well-Known Member

    How many rads on the 22mm section and how many on the 15mm section?
     
  18. Ryluer

    Ryluer Well-Known Member

    18 rads T'd off 15mm? Is it at least copper?
     
  19. Barron

    Barron New Member

    Short answer NO to copper ( only copper to the rads) and NO rads off the 22mm
     
  20. Ryluer

    Ryluer Well-Known Member

    By OH you mean "other half". Who is a builder and not a qualified plumber.
    Plastic pipe lashed in and no pipe sizing carried out. Recipe for disaster.

    Good luck with 2 circulators.
     

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