Most Economic Boiler Temperature?

Discussion in 'Plumbers' Talk' started by Mosaix, Oct 17, 2014.

  1. Mosaix

    Mosaix Active Member

    Good Morning.

    I've a Worcester Bosch central heating boiler about five years old. The temperature control is a dial numbered 1 to 6 with a dotted line between the 5 and the 6.

    I read somewhere a while back that it's most economical to run a boiler at its highest temperature. However my daughter has just had a Worcester Bosch fitted with an 'e' (for economy?) next to the 4 on the dial.

    So is here any guidance for boiler temperature?

    Thanks in advance.

    Stuart
     
  2. tom.plum

    tom.plum Screwfix Select

    this question has been asked many times on here and there's no definative answer, there are 2 skools of thought,

    1. keep it high,rads get hot so room soon reaches temp and TVR's control room,boiler uses lots of gas for a short period,

    2.keep it low,rads get warm and heat room up gentally useing less gas but for longer period before TVRs control room,

    so its nuke the room or simmer it, try them both out and come back with your results,
     
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  3. If it's a condensing boiler, then the lower the better - or else it won't condense fully (take extra heat out of the flue gases, which causes the water produced by combustion to condense out.)

    However, you can't have it too low or else your rads won't heat up fast enough...

    (You can buy a 'weather compensator' for many models which will adjust the boiler setting depending on outside temp - so it'll try and keep it as low as it can get away with...)


    If it ain't a condenser, then I don't think it matters too much - unless you set it to the extremes of temperature. In theory, having it set too low will mean the rads won't get up to required temp to warm the rooms, so the boiler will run constantly, whereas having too high a temp will likely have the water kettling and not extracting all the heat from the flame so some will go out t'chimney...

    Your daughter's boiler is def a condensing type, and I assume '4' is the highest it will still condense fully at. She could tweak it lower if she likes, provided her rads still heat up adequately.

    Your W-B is almost certainly a condenser too - I wonder if that dotted line means "don't have it this high unless you really need to?!"
     
    Mosaix likes this.
  4. Hee-hee - as Mr Plums says :D
     
  5. Mosaix

    Mosaix Active Member

    Thanks Tom.

    Is there any chance that running at the highest temperature will have any long-term adverse effect on the boiler itself?

    Stuart
     
  6. Mosaix

    Mosaix Active Member

    Thanks DA.

    Yes, mine's a condensing boiler. Thanks for the advice re the dotted line. My boiler is due for its annual visit from W/B in a couple of weeks, so maybe I'll ask the guy then.

    Thanks again.

    Stuart
     
  7. The hotter you run anything, the shorter its life. The stress on boiler components ain't no exception.

    And, in a condensing boiler's world, it won't be as efficient.

    However, you do have to have it set high enough, or else it won't do the job.
     
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  8. Cool - that's what to do.

    That's just a guess from me - if you give us the model name/number, we can look up the instructions and confirm.
     
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  9. Mosaix

    Mosaix Active Member

    Thanks again DA. I'll see if I can dig out the info and come back to you.
     
  10. Mosaix

    Mosaix Active Member

    Hi, DA. Sorry about the delay in replying.

    Looking through old paperwork I actually found a brief users guide.

    The boiler is a Greenstar 30CDi.

    On Page 16 under Tips On Energy Saving it says 'The Central Heating Control on the boiler should be set to the maximum rated temperature of the central heating system'.

    And on Page 14 under Setting The Boiler Temperature it says 'Turn the heating temperature control to the desired level between 40c and 90c'.

    I take it that means that maximum temperature of the boiler is 90c. The only reason I can see not to run the system at 90c is if there are any young kids around who might burn themselves.


    Stuart
     
  11. Steambod

    Steambod New Member

    So, the 1938 Marshall steam boiler I play with should be run at a lower temp to prolong its life? :)

    I've a new Vaillant combi at home. Normally I run it at about 50-60C but depends on how warm the house is feeling so I tend to tweak the boiler stat as and when. Last couple of rads I've replaced in the house I've put in larger (oversized) ones so running the system at lower temps doesn't mean less heat.

    If your boiler isn't doing hot water and is suitable for condensing I'd turn it down to the lowest level you are happy with, though this will change depending on weather. I've had teachers phone me up in the past complaining that their classroom heating isn't working and they are cold. When checked the classroom is actually jumping at 85F but either (1) the person has put their hand on the radiator which has turned off on the TRV or (2) they've looked at the little cheapo present-from-Clacton thermometer where the bit of cardboard with the bulb on has dropped 1/4". Result: radiator is cold/temperature is low therefore I am cold. :oops:
     
  12. Dan888

    Dan888 New Member

    This guide from WB states the following: www.worcester-bosch.co.uk/support/literature/download/F8716104727
     
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  13. Dan888

    Dan888 New Member

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  14. Jimbo

    Jimbo Screwfix Select

    If the system were to have a thermostat with weather compensation fitted, this works by reducing the flow temperature of the boiler so matching the output of the radiators, proportionately, to the temperature difference between inside and outside. Most systems are designed around a difference of about 22*C, i.e. -1*C outside temperature. When it's 10*C outside the system needs to produce only about half the temperature rise on the radiators.

    To the original question, what is important is that the return water temperature is always below the condensing temperature of the fuel in question - for natural gas this is about 55*C and for oil a bit lower like 48*C. If the water is hotter the condensing won't occur and the running costs and CO2 produced will be higher for the same output.
     
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  15. Baxi Boy

    Baxi Boy Active Member

    Aim for the return temperature to be just under 55 degrees,depending on the size of the system that would gives flow temperature of 62 -65 degrees when fully warmed up.
     
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  16. Mosaix

    Mosaix Active Member

    Thanks, everyone.

    Dan, When I set the control to 4 the boiler modulates at 58/59 rather than the suggested 68.

    I note that the download document is for a Greenstar Si whereas my boiler is a Greenstart 30 CDi so I suppose the controls may be different. I'm going to try 4.5 and see how it modulates then.
     
  17. Mosaix

    Mosaix Active Member

  18. Jimbo

    Jimbo Screwfix Select

    Clip on pipe thermometer on the return pipe at the boiler or an infrared thermometer on that pipe (pipe needs to be painted or a black sticker applied)
     
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  19. Mosaix

    Mosaix Active Member

    Thanks @Jimbo.

    Found this. Doesn't seem to be too pricey and maybe a bit easier to use than a clip on. https://www.screwfix.com/p/magnusson-im23-infrared-non-contact-digital-thermometer/1352x

    4.5 setting modulates at 63/64. Will leave at that for now then check the return temp etc. when I get the digital thermostat.

    Thanks, everyone.
     
  20. MGW

    MGW Screwfix Select

    2014 thread, and in last 5 years things have changed, but there are a few things to consider.

    1) Does a modulating boiler have a sweet point? I remember a debate about if hard or soft wood best in a wood burner, and it turns out it depends on the design of the burner, the same applies to other fuels, one boiler may be most economic when at mid point, one at max, and another at min.
    2) What effect does the dial actually have? If the boiler is connected to an OpenTherm thermostat then the dial may do very little.

    So with a modulating boiler I think the advice must be to allow it to actually modulate, be it by the return water, or by connection to eBus the last thing you want to do is switch it off/on, you of course do need to turn it off, but not until fully modulated.

    With a non modulating boiler turning the temperature down will cause it to cycle more, and turning it up, it will cycle less, each time it cycles heat is lost, but if the cycling has too big of a gap then the hysteresis increases so each time it over shoots you loose more heat.

    A TRV takes time to open/close if the boiler is off too long then the TRV is wide open when it next fires up, so it can over shoot, so now the lock shield valves needs adjusting to stop the over shoot.

    So with a non modulating not easy, as measuring temperature feed and return the boiler needs to be running, and had time to stabilise, all TRV need to be wide open to ensure pressure is constant, and although 15 deg C differential may be a good start point, some rooms will need adjusting because radiator larger or smaller than rest.
     
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