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Getting enough Hw or temp in cylinder? Condensing boiler

Discussion in 'Plumbing and Central Heating' started by tpv01, 31 Jan 2021.

  1. tpv01

    tpv01

    Joined:
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    Location:
    London
    Country:
    United Kingdom
    Worcester 27 Ri 27 kW
    Grundfos UPS3
    3 port valve with bypass to 3 towel rails (one with TRV)
    Hot water cylinder with 2 coils (solar thermal to the bottom)
    Cyclinder stat (set just over 60 Deg C)
    Hive controls
    Shower pump taking off about 2/3 from top of cylinder.

    hi all,

    have a condensing boiler put in to replace a very old feroli non-condensing. New pump. new cylinder (180 L I think. Same size as previous one).
    Heating is ok but have a question about getting enough HW and getting to temp in the cylinder.
    Running the boiler on HW only seems to cause the boiler to peg out every 5 mins. Take 5 mins to cool down and go again. End result is never really get to a good temperature and feels like it is only the top of the cylinder that gets hot so when that “layer” is used up it gets freezing cold.

    No idea how you could get the whole cylinder to 60 and hold it there for an hour to kill all the bugs.

    feels like the boiler doesn’t like getting too hot so when the return temp gets warm, and there is little flow as it’s just around the hot water circuit, the internals get too hot and it trip.

    as it continues to circulate it does cool itself down to fire again but in the process it is taking heat OUT of the cylinder to push it out of the towel rails or flue. So 1 step forward, 1 step back!

    the only two controls there seem to be the pump setting on the USP3 and the unmarked heat setting dial on the boiler. I have some temp probes set up on the inlet and outlet copper pipes on the boiler and cylinder to give me a rough I idea of the temp. I can get the boiler to output at about 62 max and once the return gets to about 48 it will trip off. At the cylinder it is a solid 60+ on the inlet (64-ish. May have that probe shielded better than the boiler one) and 50 on the outlet.

    the outlet of the cylinder sits just above the stat placement in the cylinder which is about a third up from the bottom.

    how can I set up to make and hold enough hw??
     
    Last edited: 31 Jan 2021
  2. sxturbo

    sxturbo

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    Sounds like the maximum temp has been set so it's in condensing mode permanently which is no good for the hot water.

    Maybe the unit requires a return delta of 20 degrees, unlike the traditional 12 degree differential.

    In the manual it states maximum out in KW for certain temp ranges

    50/30
    60/40
    And 80/60

    Have you tried turning the max temp up?

    Also how many rads on your system?

    I'm wondering if 27kw is to big for your system.

    Hopefully someone who knows these boilers will be along soonish
     
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  4. tpv01

    tpv01

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    This is a good help. thanks.

    I’d love it to be in condensing mode the whole time as keen to get the max efficiency but for now, and until I can rely on the solar thermal to help out more, I need to just find a setting that means my wife can have her evening shower without it going cold.

    12 rads in 4 bed house. I pushed for a smaller size as this was replacing a 32 kW but it didn’t seem worth going down any further than 27.

    I can go to all the way to max on the boiler dial. I’m about 80% round to max anyway. Isn’t being at the max like a test mode and you wouldn’t want to be there normally or is it fine to crank it right up? Are you saying I should be able to achieve 80 out and 60 return at that max?
     
  5. sxturbo

    sxturbo

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    Location:
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    Yeah according to the manual the max temp is 86.

    I can only say to turn it up and see if it makes a difference.

    Unfortunately you have purchased the wrong boiler and controls for what you want to achieve.

    To get what you want you should have gone opentherm with hot water priority.

    That means when in heating mode the boiler will always be at maximum efficiency. And when heating the hot water the max boiler temp will be called for to heat the cylinder up as quick as possible.
     
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