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Intergas OpenTherm Cycling

Discussion in 'Plumbing and Central Heating' started by andyman5002, 13 Nov 2019.

  1. andyman5002

    andyman5002

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    Hi All,

    I had an Intergas boiler fitted probably three years ago now along with a Nest v3 for the OpenTherm functionality.

    I have long suspected that its not been modulating correctly / short cycling but I could be wrong.

    I have been monitoring the flow and return temps from the boiler for a few days. The boiler seems to come on every 10 minutes (possible anti-cycling setting) for anywhere from 2-5 minutes. This can be longer when the boiler first fires up in the morning but that's the average - see the graph.

    Does this look normal? Should it be coming on this frequently? To me it would make sense, if the nest is calling for a 40 degree flow, to modulate down to the lowest output and burn for a longer period of time?

    The graph attached is for a 20 degree room temperature and the room was at 20 degrees so its just maintaining this temperature really.

    Could adjusting the max CH output parameter help with this? It seems the flow temp is rising too quickly?

    Bit of a nit picky post! I just don't really understand what the Nest/Boiler is trying to do!

    Cheers
    Andy
     

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  3. muggles

    muggles

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    Nest requires a degree of setting up to make its OpenTherm work properly. You need True Radiant turned on, but with an anticipation period of not longer than 2 hours. Bit more info here https://support.google.com/googlene...j2edzYf_pluA5CcAQxZAv4h4CtJ3VJutZTmSKKly1QRsM

    Are you sure it was actually wired up to operate on OpenTherm? It requires different terminals to be connected at both the Nest Heat Link and the boiler
     
  4. Paulj48

    Paulj48

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    Have you worked out the total KW of all your radiators, or at least the ones that are still on via the TRV (at 40 degree flow rate and not the manufacturers flow temperate rate) and compared this with the minimum output your boiler can modulate down to?
     
  5. andyman5002

    andyman5002

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    I believe it was wired correctly, TrueRadiant is turned on, I think with 3 hours rather than 2 so I can change that. I have also ordered a OpenTherm gateway to try and 'sniff' what commands etc are being sent and received if any. The Nest doesn't really expose the set point or any details around what it is doing and I am hoping the OpenTherm gateway will assist with that.

    I haven't done that in any great detail really. I did a rudimentary calculation but nothing exact (taking into account the rated kw rather than at 40 degrees) And came to around 8-10Kw excluding the ones isolated via TRV. Including those its probably about 14kw. Which is not a lot considering its a HRE 28/24, I think the lowest it will go is 7.7Kw but should this not be automatic if the Nest sets the water temp? I am tempted to force this via the parameters and see if that makes a difference, it would at least prove that boiler is or isn't modulating?

    Thanks for the help.
     
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  7. Paulj48

    Paulj48

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    I presume you have a largish house if those ratings are correct. FYI my 3 bed semi with extension has 10 rads equating to approx 17kw at manufacturers figure, at a 40degree flow rate they are rated at 5kw, we'll below my minimum of 7kw boiler.

    I have a nest V3 and it requests a flow temperature of 30 degrees in milder weather. I've got my boiler to ignore requests this low and to supply 40 degree water instead.
     
  8. andyman5002

    andyman5002

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    Hmm thats interesting, think I will have to redo my calculations with a 40 degree flow then. Same size of house as you, but as I say that was the manufacturer ratings that came to about 14kw. I will re do the calcs and see where I get to.
    How did you work out what Nest had set the temp to? I can't easily get to that info unless I'm missing that info somewhere. How often does your boiler cycle at 40 degrees? I guess I'm trying to understand if its normal. If it is great, I will just leave it alone. I dont have any issues with heat, was just concerned about efficiency / wear and tear. I would have just liked to see a longer burn maybe 20 mins so it can get into its full condensing mode etc.

    Cheers
    Andy
     
  9. Paulj48

    Paulj48

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    I read your reply wrong and thought your rating where based on 40 degree water.

    First things first, I'm not a plumber or heating engineer just an avid DIYer and technology geek.

    I have an Intergas Eco RF30 (18 month old) when the Nest requests a flow temperature its displayed on the boiler display, it normally starts between 65 and 50 depending on weather and setpoint (don't think I've seen it more that 65) and requests all the way down to 30.

    I had (and still have) the short cycling you describe that's why I changed my minimum flow to 40 but it still happens, that's what prompted me to do the calculations at various flow temperatures, and like I said my flow at 40 degrees is 5kw on a boiler with a minimum output of 7kw.

    Not sure on the long term effects of the cycling (and how much gas is wasted when the combustion chamber is blown clear of gas every time) but would certainly be interested.
     
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  10. andyman5002

    andyman5002

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    Same as you mate, basically an IT geek with a bit of spare time hence the silly graphs!

    I've never been able to actually determine what the nest has been setting it at, think my boiler is a bit older maybe and it doesn't display it on the front. I made up some pipe clips with temp sensor built in, hooked up to a raspberry pi and then piped that out to an SQL database for graphing.

    Going to try setting the modulation level tonight to see how that looks but sounds like we have very similar systems.....
     
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