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Heat-only or combi boiler for existing CH/DHW system?

Discussion in 'Plumbing and Central Heating' started by ed110220, 29 Nov 2013.

  1. ed110220

    ed110220

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    Can anyone tell me if it's significantly simpler/cheaper to install a heat-only boiler for an existing central heating and hot water system than a combi boiler?

    At the moment we have a Baxi Bermuda back boiler and 8 mm microbore central heating system with a vented cylinder.

    I'm thinking of either replacing the back boiler with a heat-only boiler and keeping the cylinder and central heating system, or replacing the back boiler with a combi boiler and getting rid of the cylinder but retaining the central heating (minus the circulation pump).
     
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  3. Dan Robinson

    Dan Robinson

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    Hang on.. i need my piece of string.
     
  4. ed110220

    ed110220

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    I wasn't asking for an exact cost, just if the one tends to be simpler and cheaper than the other in general, which doesn't seem an unreasonable question.
     
  5. kidgreen61

    kidgreen61

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    A lot of knowledgeable people on here would advise you to keep your back boiler because of it's simplicity.

    I happen to agree with them

    Maybe you need to upgrade some controls?
     
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  7. rich4nancy

    rich4nancy

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    Almost impossible to say without seeing it. For example is your current set up gravity or fully pumped?? You may need to upgrade - this is ££££ where are u planning putting the new heat only boiler ? It Will need new gas supply and new connection to primary circuits - again ££££. Tear the lot out and put a combi in could be simpler but again hard to say, have you got sufficient water pressure for a combi ? How many bathrooms etc? (Water demand) and pressurising an 8mm micro bore system could be risky as well. As Dan said how longs a piece of string?? You need to get someone round to have a butchers I think...
    Cheers
     
  8. ed110220

    ed110220

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    I was, and I would, but the air vent it needs being non-room sealed lets in a horrible draught in winter and makes the living room uncomfortable. Plus having a 100 cm^3 hole in the wall pretty much negates any draught proofing and insulation!
     
  9. ed110220

    ed110220

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    It's a fully pumped system. The logical place for any replacement would be upstairs from and almost directly above the existing back boiler, next to the existing hot water cylinder (heat only) or in its place (combi) as that is where the pipework is and directly above the gas supply. There is a large boxed-in flue through which all the pipes run from downstairs to upstairs so access isn't a problem. However the house construction makes putting the pipework elsewhere impractical.

    There is only one bathroom and water pressure doesn't appear to be a problem. I didn't know pressurising an old 8 mm system may be a problem so that's good to know - I'd like to have at least some idea before I get someone out!
     
  10. ed110220

    ed110220

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    You're right about needing new controls. Originally there were no TRVs. I have replaced the oldest radiators which had no fins and a funny connection that had the inlet and outlet at the same point and fitted TRVs to all radiators except the one next to the thermostat.

    The thermostat is a wired British Gas RS1 in the hallway and the controller is a Potterton EP2002 (also wired) in the living room.

    I'd prefer the thermostat to be in the living room as that would be more useful I think. Something that would work with the present system but also be compatible with an upgrade would be good.
     
  11. DIYnot Local

    DIYnot Local

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