Evohome - boiler on VERY frequently

Collapse
This topic is closed.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • garmcqui
    Automated Home Guru
    • Jan 2015
    • 119

    Evohome - boiler on VERY frequently

    Hi all,

    I installed an Evohome system a few months ago, it is an S-plan system with one BDR-91 controlling the zone valves for heating, and another controlling the zone valve for hot water. The zone valves then activate the boiler.

    The zoning is working well, however with different rooms calling for heat all the time, the gas condensing boiler has been coming on very frequently and often only runs for a few mins. Since it has a pump overrun feature, the over run is almost always on.

    Is this the way it should be? Or what is wrong with the system? Could it be that it needs another BDR91 controlling the boiler directly, for which I believe the number of boiler demands per hour can be limited?

    Thanks in advance,

    Gareth
  • top brake
    Automated Home Legend
    • Feb 2015
    • 837

    #2
    sounds like you might have the relays bound incorrectly.

    can you describe the process that you went through to install the evo and its BDR91, and add the hot water kit?
    I work for Resideo, posts are personal and my own views.

    Comment

    • Rameses
      Industry Expert
      • Nov 2014
      • 446

      #3
      The evohome throttling the heat in the boiler is normal (400 degree's is only needed in short bursts), the pump continuing to take the heat from the exchange is also nothing to worry about (German systems do this all day long), the in & out temp measurement also guide the boiler firing, so the boiler manufacturer will also be 'overiding' the BDR's request, if it feels there is enough heat to exchange.

      If the overrun is truly always on then as TopBrake says could be a double bind etc. Or we have seen instances where the signal wire was wrongly wired (know this from personal experience)
      getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

      Comment

      • garmcqui
        Automated Home Guru
        • Jan 2015
        • 119

        #4
        Thank you for your replies.

        Paring was definitely carried out as per the instructions. The BDR91's definitely switch on and off as they should, heat is only called for when it should be. The overrun isn't actually always on, just on a lot.

        I was just worried that the boiler seems to be much more active than it used to be with the old non-zoned system.

        If it's not a problem, I won't worry about it.

        Thanks

        Comment

        • top brake
          Automated Home Legend
          • Feb 2015
          • 837

          #5
          Originally posted by garmcqui View Post
          Thank you for your replies.

          Paring was definitely carried out as per the instructions. The BDR91's definitely switch on and off as they should, heat is only called for when it should be. The overrun isn't actually always on, just on a lot.

          I was just worried that the boiler seems to be much more active than it used to be with the old non-zoned system.

          If it's not a problem, I won't worry about it.

          Thanks
          Have a read of this FAQ

          I work for Resideo, posts are personal and my own views.

          Comment

          • garmcqui
            Automated Home Guru
            • Jan 2015
            • 119

            #6
            Fantastic, thanks.

            So I presume the HR92 TRV's have TPI functionality?

            Comment

            • top brake
              Automated Home Legend
              • Feb 2015
              • 837

              #7
              Originally posted by garmcqui View Post
              Fantastic, thanks.

              So I presume the HR92 TRV's have TPI functionality?
              The Evohome system is TPI, HR92 are combined sensor and actuator units controlled by the Evohome controller. The BDR91 wireless relays are also controlled from the Evohome controller.
              I work for Resideo, posts are personal and my own views.

              Comment

              • Rameses
                Industry Expert
                • Nov 2014
                • 446

                #8
                Originally posted by garmcqui View Post
                Thank you for your replies.

                Paring was definitely carried out as per the instructions. The BDR91's definitely switch on and off as they should, heat is only called for when it should be. The overrun isn't actually always on, just on a lot.

                I was just worried that the boiler seems to be much more active than it used to be with the old non-zoned system.

                If it's not a problem, I won't worry about it.

                Thanks

                I totally understand. Very similar to start/stop in modern cars - its more efficient to let the boiler fire occasionally when required - than all the time (like old controls did).

                Because of new systems and newer controls and more information (like exact set points and temps) this leads to (completely justified) questioning. We have been conditioned to accept heating as this thing that our 'Dads' controlled with iron will, went on and off - and we just either froze or boiled, with Dads armchair the only place in the home 'just right' - and we just accepted it. Through more intelligence, greater sensing and giving better information (plus a drive to save money), leads to many questions - ALL of which we will try to answer.

                Just an additional note - we see many boilers / systems do this when there is a small load/demand. So if you have only one room 'alive' in a four bed house (where the boiler has been sized for this) - it makes sense the system, accommodates this, rather than in the old days the boiler would continue to heat the circuit and try an dispel the heat any way it could.
                Last edited by Rameses; 12 March 2015, 08:15 PM.
                getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

                Comment

                • SteveP
                  Automated Home Guru
                  • Dec 2012
                  • 190

                  #9
                  I had the same issue with my boiler when I installed Evohome. I first noticed the issue as the rads never got up to a decent temperature and so some rooms didn't heat up properly. I found that it was called short cycling and the following link identified the issue and solution. http://vaillantcyclingproblem.blogsp...parameter.html. Basically what happens in a modern boiler is that when there is a small demand on the boiler it checks the flow and return temperatures and as soon as they get within a certain amount of difference the boiler says that the heat is not being used and so stops firing. When there are only a few rads on then this happens a lot. The boiler then waits a predetermined length of time before firing again (Based on an algorithm as in the link). The link identified that the actual length of time the boiler waited was dependant upon the temperature setting of the boiler. So at a low boiler temperature setting the algorithm says wait 20 minutes before firing. That was causing the boiler to never reach its full temperature if the weather was very cold. However, turning up the boiler thermostat to max makes the boiler only wait 1 minute before re-firing. This cured the problem and the rads all reach their correct temperature. The only downside is (as you have observed) the boiler pump is always on over run (which is 10 mins on my boiler) and the boiler fires in short burst and very rarely shuts down until all rads are set back overnight.

                  Comment

                  • top brake
                    Automated Home Legend
                    • Feb 2015
                    • 837

                    #10
                    Originally posted by SteveP View Post
                    I had the same issue with my boiler when I installed Evohome. I first noticed the issue as the rads never got up to a decent temperature and so some rooms didn't heat up properly. I found that it was called short cycling and the following link identified the issue and solution. http://vaillantcyclingproblem.blogsp...parameter.html. Basically what happens in a modern boiler is that when there is a small demand on the boiler it checks the flow and return temperatures and as soon as they get within a certain amount of difference the boiler says that the heat is not being used and so stops firing. When there are only a few rads on then this happens a lot. The boiler then waits a predetermined length of time before firing again (Based on an algorithm as in the link). The link identified that the actual length of time the boiler waited was dependant upon the temperature setting of the boiler. So at a low boiler temperature setting the algorithm says wait 20 minutes before firing. That was causing the boiler to never reach its full temperature if the weather was very cold. However, turning up the boiler thermostat to max makes the boiler only wait 1 minute before re-firing. This cured the problem and the rads all reach their correct temperature. The only downside is (as you have observed) the boiler pump is always on over run (which is 10 mins on my boiler) and the boiler fires in short burst and very rarely shuts down until all rads are set back overnight.
                    Interesting thanks for sharing. No such behaviour on my Vaillant ecotec plus 615. Boiler set to run at 70deg
                    I work for Resideo, posts are personal and my own views.

                    Comment

                    • jonstatt
                      Automated Home Guru
                      • Feb 2015
                      • 111

                      #11
                      There is a potential for continual short cycling as follows:-

                      1) Only one or two rooms need heat therefore the loop of water being heated is small
                      2) With a boiler that only has no modulation (either on or off), then it is heating that water as fast as it possibly can. It will get up to temperature quickly causing it to stop and go into pump-overrun. For most boilers that is around 2 minutes. Then it fires up again to top up the heat which will be a short run..followed by over-run
                      3) When the HR92 detects that room temperature has been reached, it goes into a "sustain" mode. It does this by flicking the BDR91 relay for short periods.
                      4) When you overlay 2) and 3) together, you get a lot of on/off cycling

                      I never thought much of this to start with because I assume modern boilers are designed for continual on/off and it has no real relevance. However, EVOHOME when configured in a different way has the ability to increase the minimum run time of 3) and the number of times it will do so in an hour. Even with this capability, the very fact you have a boiler designed for a large loop, heating up a much smaller one now, means that boiler will be cutting in and out over and over regardless.

                      So the question is? Do we save ourselves a load of money with reduced gas usage.....and get enthusiastic nods from green enthusiasts....only to be clobbered with a 2000 pound replacement boiler bill 5 years earlier than expected?

                      Comment

                      • orange
                        Automated Home Guru
                        • Dec 2014
                        • 149

                        #12
                        Originally posted by jonstatt View Post
                        So the question is? Do we save ourselves a load of money with reduced gas usage.....and get enthusiastic nods from green enthusiasts....only to be clobbered with a 2000 pound replacement boiler bill 5 years earlier than expected?
                        absolutely !

                        there is a setting (in advanced settings) called "min on time" mine is set to 5 minutes. I assume this is a minimum boiler on time ? I also assume this is to prevent short cycling with point 3) ?

                        either way it's ignored in my setup as I get lots of 1 minute type boiler demand (you can tell it's boiler demand as the green light in the BDR91 lights up). Support haven't responded to my requests for clarification on this so I guess we'll never know.

                        Comment

                        • Rameses
                          Industry Expert
                          • Nov 2014
                          • 446

                          #13
                          The BDR91 makes a call for heat. The boiler is in control of how it fires. Whilst the 'green light' is on - this does not mean that the boiler needs to operate as the BDR tells it. The thermostat calls for heat, the BDR91 interprets that call, the boiler then chooses what to do with that call. The fact that the minimum 'on' is 5 mins - has nothing to do with the boiler firing. This is controlled by the boiler logic and circuits. An old cast iron boiler has no PCB so it will be very 'dumb' - a newer system will have a lot more intelligence.

                          (Note: we see some older boilers take 45 secs to just heat up and fire - when min settings are set to 1 min - this means that the system only has 15 secs of heat to apply - just a note as this can make the system appear like it is more on & off than usual - again a reference to the boiler / manufacturer controls is useful here)

                          Set parameters within the boiler itself ( modern high efficiency combi boilers , you can set a limit on the short cycling for example) can be tweaked (if you know what you are doing)

                          To get this very very very granular level of control then a 'figure 4' setup is optimal (see appedix of the manual). (removes the heating valve from the Splan level and controls the system using the boiler relay)
                          Last edited by Rameses; 13 March 2015, 10:42 AM.
                          getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

                          Comment

                          • garmcqui
                            Automated Home Guru
                            • Jan 2015
                            • 119

                            #14
                            Some very interesting information here. Am also reading through thw following post with interest, as it seems to be a similar problem:



                            Might seem like a daft idea, but last night I set up a video camera to record the status display of the boiler all night. I will review the footage in more detail this weekend but from a quick glance this morning, it seems the boiler is coming on for approx 1 minute every 10 minutes, all night. All HR92's were set to 5C overnight except our bedroom, which was set to 18C (we have a 4 week old baby so room needs to stay warmish).

                            Also, had a quick look in the advanced settings. Am I right in thinking that as I don't have an actual boiler relay (boiler controlled by zone valves) then I can't set variables such as the cycle rate and minimum on time?

                            Comment

                            • erik
                              Automated Home Guru
                              • Feb 2015
                              • 244

                              #15
                              Rameses: isn't orange saying he often sees the BDR91 light coming on for 1 minute even though minimum on time is set to 5? Regardless of what boiler is connected and regardless of what logic/intelligence is built in the boiler, that bdr91 behavior is just wrong.

                              I personally haven't seen this behavior by the way. When I have set minimum on time to 2 or 3, it usually respects that setting.

                              Comment

                              Working...
                              X