Central Heating Pump

Discussion in 'Plumbers' Talk' started by nodrog38, Apr 2, 2019.

  1. nodrog38

    nodrog38 New Member

    Can anyone help.
    I need to replace my boiler but I have an issue with the circulating pump.
    Due to the size of the system the circulating pump is a GRUNDFOS UPS 25-80 180 235Watts and I can not find a boiler to take this size of pump.
    I want to replace the boiler with a Worcester Greenstar 40CDi Regular Boiler but it can only take an 80Watt pump. Worcester technical help said I can use a relay but they could not give details.
    Does anyone have a wiring diagram for doing this and what type/size/make of relay should I use.
     
  2. sam spade

    sam spade Active Member

    You may not need such a large pump, or boiler.

    Tell us more about your system - how many rads, size of HW cylinder etc. How big is your house, no of baths/showers?

    Is the house well insulated or do you have problems heating it when it is very cold (below 0C)?
     
  3. nodrog38

    nodrog38 New Member

    Hi sam, there are 25 radiators, 250L hot water tank. The house is large, 3 floors with 14 rooms which includes 2 bathrooms and en-suite. There will be 3 baths and 3 showers. At present the house is being renovated so not sure what it is like trying to heat when cold
     
  4. sam spade

    sam spade Active Member

    As you don't know if the existing boiler and radiators are the correct size, it might be a good idea to carry out a heat loss calculation, taking into account any improvements in insulation you intend making. I suggest you use https://www.myson.co.uk/hlm/

    The first page allows you to set some constants. The Heat Up Factor of 20% is fine if the house is only heated morning and evening. But if it is occupied all the day it can be reduced to 10%. The Mean Water Temperature should be changed to 60C. This will allow the boiler to condense more often as the return temperature will be no higher than 50C (Assuming a flow of 70C and differential of 20C). The MWT affects the physical size of radiator required as the output of a rad is dependent on the flow and return temperatures.
     
  5. nodrog38

    nodrog38 New Member

    Thanks for the info. Im going over on Thursday so will do the survey.
    Many thanks for your assistance.
     
  6. nodrog38

    nodrog38 New Member

    Hi Sam,
    I used the attached link today and have attached the results.
     

    Attached Files:

  7. gas monkey

    gas monkey Well-Known Member

    Put in two compies
     
  8. nodrog38

    nodrog38 New Member

    Would be easy but want to keep s plan as i have
     
  9. gas monkey

    gas monkey Well-Known Member

    Lot cheaper to run
     
  10. nodrog38

    nodrog38 New Member

    Aye but then i would need electric showers.
     
  11. gas monkey

    gas monkey Well-Known Member

    No
     
  12. nodrog38

    nodrog38 New Member

    would i get enough pressure to run a shower, can you fit a pump ?
     
  13. gas monkey

    gas monkey Well-Known Member

    Pressure check from water company if ok the world's what you want it to be
     
  14. nodrog38

    nodrog38 New Member

    ok will check and see
    Thanks
     
  15. gas monkey

    gas monkey Well-Known Member

    He who dares makes life worth living you will do fine
     
  16. The Teach

    The Teach Screwfix Select

    A low loss header may be the answer :)
     
  17. sam spade

    sam spade Active Member

    Sorry for the long delay; I didn't receive any notification from the Forum.

    So your heatloss is about 28kW, including 20% warm-up allowance; which means you do not need a 40kW boiler. What about the hot water? That's easy. You just time the hot water to come on when the heating demand is low or non-existent, e.g overnight, during the afternoon or when the heating is not required. The full 28kW is then available for hot water. A modern well insulated cylinder will retain its heat for many hours.

    1. What is your existing boiler?
    2. Do you know the kW ratings of your rads?
    3. What speed setting is your UPS 25-80 on?
     
  18. nodrog38

    nodrog38 New Member

    Hi Sam,
    the boiler that was in was U/S, it was beyond repair. It was a glow warm 38hxi regular boiler.
    The rads have ben removed, 22 of them, they were old heavy rads with a lot of corrosion.
    The speed setting of the pump is 3.

    The old boiler was in the kitchen, they had ran 35mm feed and return from the boiler up to the pump in the airing cupboard which is next floor up from the boiler, a run of 20m. after the pump the pipe work reduced to 22mm and continued like this round the house back to the airing cupboard, increased to 35mm then back to the boiler. The hot water tank is a Tornado Stainless 250L (Telford Stainless Products).
     
  19. sam spade

    sam spade Active Member

    I suspect that the Glow-worm 38hxi replaced an old non-condensing boiler which operated with a flow/return differential of around 10-12°C. This would explain the use of 35mm pipe between boiler and upstairs. If a 20°C differential is used the pipe only needs to be 28mm. I doubt if the system was rebalaned to a 20°C differential, which would explain the UPS 25-80 pump.

    The Tornado 250 litre cylinder has a 25kW rated coil, which means a 28kW boiler would be more than adequate if HW is timed when there is nil or low CH requirement.

    I tried to get onto the Grundfos website, to check the UPS 25-80 curves, but it's down for maintenance. Will try again after the holiday.
     
  20. nodrog38

    nodrog38 New Member

    If i eat meat, which i do, and lots of it, it has sod all to do with you, so keep your nose out of my business. I have absolutely no time for people like you.
     

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