Central heating problem

Discussion in 'Plumbers' Talk' started by hbviva, Apr 20, 2019.

  1. hbviva

    hbviva New Member

    I was wondering if any heating system experts can help ;
    I have a conventional balanced flue boiler that heats a series of radiators and an indirect cylinder for hot water . 4 pipes on boiler , 1. 15mm feed from tank in loft 2. 22mm vent pipe to top of tank 3. 22mm to radiators & 4. 22mm pipe from the top of the boiler that goes to a SMC commodore controller .This unit has a further 2 outlets ....one goes up to the hot water indirect cylinder and the other goes straight into a grundfos circulation pump which in turn heads off to radiators .What can I replace the obsolete smc unit with. I’ve done some heating /plumbing before on a diy basis so I consider myself reasonably competent but not so hot in system design.Any help/advise will be gratefully received
     
  2. kiaora

    kiaora Guest

    Hi
    How about say a new pump, feeding 2 new zone valves? 1 heating and 1 hot water ?
    Make sure you allow for feed and vent to the boiler

    Good luck
    Peter
     
  3. hbviva

    hbviva New Member

    Thanks Peter for the reply. I'm not totally sure what the original smc commodore controller does, it looks like a circulating pump but has 3 unions on it . I thought it was a pump with a built in diverter valve but it has only 3 wires to it ( L,N & E) so I guess it cant be . I thought I could replace it with a 3 port valve but they seem to have 5 wires.If I take up your suggestion ,I assume the 22mm from top of boiler would go into a pump then 22 out to a tee , then two 2 way zone valves on each side of the tee , one to hot water and one to rads . How would I wire them in though ? I only have 3 cables from wall at the moment each are 3 wires (L,N & E) One goes to smc , one goes to boiler and the other goes to grundfos pump.I wasn't planning on re-wiring the whole system. I'm having to replace the boiler due to it springing a leak so thought I would change pump and smc at the same time as both are looking worse for wear.
     
  4. kiaora

    kiaora Guest

    Hi
    It’s quite easy to wire the pump, boiler and zone valves, if you can understand the basics,

    You need a wiring center, and some 1.5mm 3 core flex.

    There are diagrams on line to follow, or I , or others can explain how it works .

    Each zone valve has 5 wires, green/yellow earth, grey permanent live, orange switch live , blue neutral and brown to open the valve.

    So when the valve is called ie. heating, the brown becomes live and opens the valve, a micro switch make between the grey and orange, and the orange fires the boiler.
    Good luck
    Peter
     
  5. kiaora

    kiaora Guest

    What you have now is basically, two pumps, one Heating one hot water
     
    The Teach likes this.
  6. The Teach

    The Teach Screwfix Select

    Could be a vintage Smc twin pump system :( if it is central heating has its own pump and hot water heating also has its own pump.

    They will all be replaced with an up to date control system,standard practice :)
     
  7. hbviva

    hbviva New Member

    Thanks for your help gents , I think I will replace it with Peter’s suggestion which I believe is called an S type system . I have a few questions that you may be able to answer .
    1.My existing set up (conventional floor standing boiler with 4 outlets) has the smc and grundfos pumps in tandem from the top of the boiler pumping downwards . I read somewhere that this shouldn’t be done . Is this a no no ?
    2. On the hot water flow from the boiler ,should this go to the top of the indirect cylinder or the bottom?
    3. Should the pump be sited in the flow or the return pipe work ?
    4. Do I need one or two pumps in tandem (4 bedrooms, 2 bathrooms 3 reception ) or will a good quality grundfos be sufficient?

    Dave
     

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