Boiler coming on for just a few seconds

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  • paulockenden
    Automated Home Legend
    • Apr 2015
    • 1719

    #16
    No answers yet.

    I do understand the TPI can result in the boiler only firing for a short time, but in my case it sometimes comes on for such a short time it doesn't even ignite!

    If you have a system with a boiler relay then you can adjust the parameters so that this doesn't happen, but if you've got an S plan setup (which doesn't have a boiler relay) those parameters aren't used.

    My current thinking is that that's possibly a mistake (certainly a shortcoming), and that the system could be improved if logic was added such that the minimum on and cycle timings were available in an S Plan setup.

    Anyway, I have the experts coming to take a look a look on Friday, so I'll know more after that.

    DESPITE that little niggle, I still think Evohome is great. My house feels much more comfortable than it did with the old heating controls.

    P.

    Comment

    • f1arp72
      Automated Home Jr Member
      • Apr 2015
      • 48

      #17
      Originally posted by paulockenden View Post
      No answers yet.

      I do understand the TPI can result in the boiler only firing for a short time, but in my case it sometimes comes on for such a short time it doesn't even ignite!

      If you have a system with a boiler relay then you can adjust the parameters so that this doesn't happen, but if you've got an S plan setup (which doesn't have a boiler relay) those parameters aren't used.

      My current thinking is that that's possibly a mistake (certainly a shortcoming), and that the system could be improved if logic was added such that the minimum on and cycle timings were available in an S Plan setup.

      Anyway, I have the experts coming to take a look a look on Friday, so I'll know more after that.

      DESPITE that little niggle, I still think Evohome is great. My house feels much more comfortable than it did with the old heating controls.

      P.
      Thanks. Yes, I do have an S Plan setup so I have no control over those parameters. I've been monitoring my boiler for last 40 minutes. It appears to come on every 10 minutes for about a minute, so it seems to be a planned scheduled thing by the controller. The thing is, it doesn't get time to heat the water so every rad is still cold so why is it doing it. Just seems a waste of energy and effort, and can't be good for the boiler. I've found another thread with other people having same issue but it was closed so I couldn't comment there, but the fact others are also experiencing the 1 minute every 10 minute issue does make it sound like an internal setting to fire up boiler 6 times an hour even of it has no effect on water temperature in rads !!

      Perhaps you would be kind enough to report back after Friday if they confirm it to be a bug, or confirm it's normal (if very strange) behaviour ?

      Comment

      • erik
        Automated Home Guru
        • Feb 2015
        • 244

        #18
        It is normal for TPI to fire the boiler every 10 minutes. It generally makes sense to do this when setpoint is reached and the system wants to keep it on setpoint. It feels much more comfortable and you can reach much more precision to have the radiator turn on for a short while every 10 minutes than to have it, for example, turn on for an hour and then turned off for an hour.

        So normally, it would be a good thing. However, if you're not able to change the minimum-on-time and your boiler requires a certain minimum-on-time, then it might get troublesome.

        Comment

        • paulockenden
          Automated Home Legend
          • Apr 2015
          • 1719

          #19
          I'm with Erik - I can see the point of the short firing that TPI brings once the house it up to temp. It's about maintaining termperature rather than heating the house up. It seems like a good idea - maintain a temp rather than temp swings that you get with conventional controls.

          It just needs tweaking, because switching on the boiler for such a short time that it doesn't fire is silly. I'd almost call it a bug.

          P.

          Comment

          • f1arp72
            Automated Home Jr Member
            • Apr 2015
            • 48

            #20
            Yes, I agree with you both. Firing the boiler to maintain the temperature at 21 is a nice idea, but .....

            a) if the temperature hasn't dropped below 21, is it really necessary
            and
            b) by the time my boiler has actually fired up after the BDR91 "goes green", I get a total of about 35-40 seconds of heat which does absolutely nothing with regards to heating the pipes or radiators. So, it's a pointless exercise with my setup. Maybe better boilers fire up immediately and you get an extra 20 seconds of heat, although I still wonder if that's enough considering I have 8 zones/radiators.

            Comment

            • paulockenden
              Automated Home Legend
              • Apr 2015
              • 1719

              #21
              The system has calculated that the 35-40 seconds of heat every ten minutes is what's required to counter the heat losses.

              Would you rather than have that or a longer burst perhaps once an hour, with the subsequent bigger temperature swings in the house?

              The more of TPI I see the more I like it, I just think it needs to be made aware of how long a boiler takes to ignite!

              Comment

              • f1arp72
                Automated Home Jr Member
                • Apr 2015
                • 48

                #22
                Originally posted by paulockenden View Post
                The system has calculated that the 35-40 seconds of heat every ten minutes is what's required to counter the heat losses.

                Would you rather than have that or a longer burst perhaps once an hour, with the subsequent bigger temperature swings in the house?

                The more of TPI I see the more I like it, I just think it needs to be made aware of how long a boiler takes to ignite!
                I like the idea of TPI but it sounds like this 10 min / 1 min cycle if preprogrammed and not calculated on the actual house/room requirements.

                Anyway, I need to try and accept this system and "let it do its thing". Weather warming a bit now, so will turn off until heating the autumn and see how I get on with it through our first winter together. It'll either stay, or end up on eBay (I hope they get a good resale value )

                Comment

                • erik
                  Automated Home Guru
                  • Feb 2015
                  • 244

                  #23
                  the TPI in itself is fine. But being able to control minimum-on-time and amount-of-cycles-per-hour is pretty important.

                  Comment

                  • Wallyİ
                    Automated Home Sr Member
                    • Jan 2015
                    • 53

                    #24
                    Originally posted by paulockenden View Post
                    The system has calculated that the 35-40 seconds of heat every ten minutes is what's required to counter the heat losses.

                    Would you rather than have that or a longer burst perhaps once an hour, with the subsequent bigger temperature swings in the house?

                    The more of TPI I see the more I like it, I just think it needs to be made aware of how long a boiler takes to ignite!
                    That's like getting up and starting your car every half hour in the winter just to make sure it's warm inside when you need to drive for work...

                    The amount of water running through your radiators is so low it should take a modern boiler no more than 5 minutes to heat up from scratch...Let alone a T° difference of a few degrees when you're in need of heat...
                    So this firing-up is totally useless and a complete waste of energy...
                    But I'm no expert...and the more I read the experts advice and comments...Evohome IS rocket science !!!

                    Comment

                    • paulockenden
                      Automated Home Legend
                      • Apr 2015
                      • 1719

                      #25
                      Originally posted by Wallyİ View Post
                      That's like getting up and starting your car every half hour in the winter just to make sure it's warm inside when you need to drive for work...
                      Imagine if that same car didn't have a variable accelerator. It simply had a binary on/off.

                      How would you do a steady 70MPH on the motorway?

                      You'd apply little dabs of power at regular intervals.

                      I think that's what TPI is trying to do. As opposed to traditional heating controls which are like allowing the car to slow down to 60, then accelerating to 80, then letting it slow back down to 60, etc. etc.

                      There's good logic there, and if you have a boiler relay you can set parameters so that your boiler cycles aren't wasted.

                      The problem is that those of us with S Plan don't get to do that.

                      P.
                      Last edited by paulockenden; 7 May 2015, 09:20 PM.

                      Comment

                      • erik
                        Automated Home Guru
                        • Feb 2015
                        • 244

                        #26
                        Originally posted by Wallyİ View Post
                        So this firing-up is totally useless and a complete waste of energy..
                        If the system was totally cold, I would agree. However, once your system and room is at temperature, it only takes a very little amount of extra energy to maintain that temperature (especially if your house is insulated). Just a minute of turning ON can easily be enough to maintain requested temperature.

                        In my case, the 1 minute of heat requested by Evohome actually added TOO MUCH heat to the system. And because it continued to go ON for 1 minute every 10 minutes, regardless of rising temperature and already being above setpoint, Evohome would build up huge overshoots in my house.

                        My old wired Honeywell Round uses TPI as well and also uses 10 minute cycles once temperature is reached (temperature within the proportional band). However, it sometimes skips a 10 minute cycle. For example: it will go ON for 1 minute, stay OFF for 10 minutes, go ON for 1 minute, stay OFF for 20 minutes, go ON for 1 minute, go OFF for 10 minutes, go ON 1 minute, stay OFF 30 minutes, go ON 1 minute, etc. This keeps the temperature almost perfectly on setpoint.

                        So the point I'm trying to make: 1 minute of heat per X minutes does not have to be a waste. It can easily be enough to maintain, or even raise room temperature.
                        Last edited by erik; 8 May 2015, 12:05 PM.

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