Radiator balancing problems

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  • DBMandrake
    Automated Home Legend
    • Sep 2014
    • 2361

    #16
    Originally posted by killa47 View Post
    Hi Securitybyte
    I sympathise with your woes as I too am struggling to stop my WB 40cdi conventional form short-cycling. WB term is on my boiler as "Gradient Limitation" - flow temperature rising too quickly.

    I wonder if your problem is to do with the parameter setting of "Anti-cycle flow temperature differential" which WB normally set as 10C. So if your return temp is inside 10C of flow temp, it will turn off the burner for 2 minutes (maybe 3 minutes depending on parameter setting).

    I have been confused for some time with whether to increase/decrease pump speed, open/shut LSV's, increase/reduce flow temperature, improve ABV function etc.
    Sounds like the same scenario as Securitybyte - assuming your pump speed is not set too low flow temperature rising "too quickly" is going to be because the radiator valves are largely closed and most of the flow is returning via the automatic bypass valve, or possibly your automatic bypass valve is set too low. What differential pressure is it set to ?

    To some degree I think this is inevitable on the Honeywell system if you have all radiators controlled (eg no bypass radiator left open) because under some conditions it will run the boiler when the HR92's are hardly open, but when it does that it generally runs the boiler at a low duty cycle. (Eg it may be turning it on for 2 minutes out of 10 minutes) But that may still be enough to trigger the "Gradient Limitation" warning on your boiler during that 2 minute period.

    I have an ancient conventional boiler that has no electronics at all apart from a retrofitted digital flow temperature controller I added to replace the original mechanical flow stat - and I see the same rapid rise of flow temperature when for example there are only 2 zones in the house active and they are already up to temperature - but my boiler doesn't care, the flow temperature controller just shuts it off when it reaches the the target temperature and doesn't complain about the rapid rise.

    The issue here really is that your boiler is being too clever for its own good - a fast flow temperature rise when all the radiators are nearly closed and the ABV is flowing heavily is to be expected. Does it actually cause a lockout situation where you have to manually reset it to get things working again, or does it just complain on the screen but continue working normally ? If the latter I probably wouldn't worry about it to be honest, if it does prevent it working I would see if there was any way to relax the "Gradient Limitation" threshold so that it doesn't get tripped.
    Last edited by DBMandrake; 4 March 2016, 01:33 PM.

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    • killa47
      Automated Home Guru
      • Jan 2016
      • 123

      #17
      Hi DBMandrake

      As always, an excellent explanation of some confusing (to a layman) operational features of our boiler systems.

      You have at the least reassured me that the gradient limitation is not something I should worry too much over. I t has done this pretty much since the Evohome was put in but at no point as it triggered a lockout.

      Equally, the boiler does not complain noise-wise nor do I have audible symptoms throughout the system. In fact, since Evohome, I enjoy having the visual control on the CH/DHW in the house.

      I did wonder about the ABV setting but this is just about the only part of the system I am unfamiliar with. I know they can be adjusted and I have a Center EHE0200281 ABV. It is adjustable and I have the install guide so I will look further at this. I suspect I might need to ask my plumber to make sure it is correctly rated for the flow rate/pump head.

      Your suggestion to relax the gradient limit also occurred to me but I cannot see a parameter for this when I checked them yesterday. Maybe WB can advise me if this is user configurable.

      Your comments are much appreciated, including those re Securitybyte, and I will digest these further.

      Many thanks

      Ian K.

      Comment

      • Securitybyte
        Automated Home Jr Member
        • Jan 2016
        • 19

        #18
        Hi Ian

        Thanks for the information. Makes me a bit happier to know it is not just me! My Anti-fast cycle flow temperature is set to the default of 6 degrees K. I assumed that was Kelvin but that would equate to -267.15 degrees C, so not sure how that works... Anti-fast cycle time is on the default of 5 mins.

        Your issue sounds pretty similar - all ok with lots of radiators on..

        I've been doing some more monitoring and have narrowed it down a bit more, and will explain this in my next post to Mandrake!

        Thanks again

        Comment

        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          #19
          Originally posted by Securitybyte View Post
          Hi Ian
          My Anti-fast cycle flow temperature is set to the default of 6 degrees K. I assumed that was Kelvin but that would equate to -267.15 degrees C, so not sure how that works...
          6 degrees will be a differential temperature, so in that regard Kelvin and Celsius are equivalent. (Unlike Fahrenheit where the units themselves are different by a 9/5 ratio, not just a different zero starting point)

          Comment

          • Securitybyte
            Automated Home Jr Member
            • Jan 2016
            • 19

            #20
            Hi Mandrake

            Thank you again for your great reply.

            When the 5 radiators were on, the two manual ones were on number 1 but got hot pretty quickly, so I think the pins were quite well open. The Evohome TRVs were all atleast a few degrees below their setpoints, so should have been fully open but I didn't check. The light was lit up on the BCR91 the whole time. I thought the valves would have been open more fully during the time it was heating up, and thus a lower return temperature. When it was up to temperature, with the valves more closed, I'd expect the return temperature to be potentially higher and thus then get the status 204. But it was the other way around.

            Opentherm sounds like it would do exactly as is needed, but unfortunately my boiler does not appear to support it

            It doesn't cause a lock out, it just gives the status and goes quieter as the burner stops. After 5 minutes or so it resumes. The Anti-fast cycle flow temperature is configurable between 2 and 15 degrees K. It's currently on 6 (Default) but I don't understand enough about it to change it at the moment..


            I balanced the radiators today. I need to do some further tweaks but most of the radiators have a drop of 9-12 degrees C. I managed to achieve this with the pump speed on low - all the radiators got fully hot, and I am pretty sure the boiler did not cycle at all over the couple of hours I was doing it. So I was quite happy with that. Afterwards though, after cooling it down and switching it all back on again - the radiators were barely hot. Strange as they were fine as I was balancing them and I double checked them afterwards. I've since re-opened them all back up by half a turn and will check what this has done to the temp drops a bit later.

            Back to running the heating with one radiator on... The zone started at 21C (hotter than normal due to the balancing). I requested 25C and the TRV claimed to be 100% open. Very shortly after the boiler starting, the flow had climbed to 73C with a return of 33C. The boiler shut off with the 204 status.

            I made the following changes to see if they would have any affect, but none of them made any difference at all:

            - increased the pump speed to 3
            - put the pump speed back to maximum
            - reduced the maximum heating output to its minimum of 7kW - just to test
            - turned up some radiators with manual TRVs

            No luck - it keeps switching off early due to the high flow temperature when the zone is still below the setpoint. I've been monitoring it since 2000. At least for the last hour it has barely stayed on for more than 10 seconds, with the zone 1/2 a degree below the setpoint the whole time.

            I understand why it is doing it, as you kindly explained, but I won't be able to rest until it stops doing it

            The last time it did it, it said the return was only 47.5C, yet the flow went right up to 70C before it switched off. So if my observations are correct, sometimes the flow temperature exceeds the setpoint because the return temperature is high. And sometimes it is because there is not enough water flow through the heat exchanger? I've turned the pump back onto maximum, but I guess if some TRVs have since closed now.. But isn't that was the automatic bypass is for? Sorry, a lot of these questions are just me thinking out loud and I'm not expecting answers to all of them.

            I've noticed another issue too. If the heating is running and I switch on another radiator in an unused room, it sends through a load of cold water to the boiler which triggers blocking error 349 - "CH: Boil Detect, large delta T despite minimum burner load". This is where the boiler is "operating at minimum burner load and there is a greater than 18C Flow & Return temperature difference". What a stupid design.

            Many thanks
            Last edited by Securitybyte; 5 March 2016, 12:45 AM. Reason: Shorten and refactor

            Comment

            • killa47
              Automated Home Guru
              • Jan 2016
              • 123

              #21
              Securitybyte

              Can I just ask how old the CH system is. Could your rads need flushing if they are quite a few years old. Have they got sludge in them and when the LSV's are almost shutdown is this restricting the flow somehow.

              Ian K.

              Comment

              • Securitybyte
                Automated Home Jr Member
                • Jan 2016
                • 19

                #22
                Hi Ian

                I had the whole system (new boiler and rads) installed about 8 months ago. They're all hot on the bottom so I'm hoping there's nothing lurking in them :S

                Good thinking though..

                Thanks

                Comment

                • Securitybyte
                  Automated Home Jr Member
                  • Jan 2016
                  • 19

                  #23
                  Hi

                  Just an update.

                  I called the helpful Worcester technical support line this morning.

                  I said about it switching off with error 349 when a cold radiator is switched on, and the fact that it doesn't seem to modulate low enough when only 3-4 radiators are switched on, resulting in status 204.

                  She said it sounds like I need a Low Loss Header? Does anyone have any experience of these?

                  I also asked about the integrated automatic bypass. She said it is very small and that I should have an additional one installed.

                  Does this mean my system was installed wrongly?

                  None of the old radiators had TRVs - I had a new boiler, new radiators / LSVs / and TRVs fitted to all radiators, and the Evohome installed, in one job. Should my installer have fitted an ABV when it was all installed? Is that not a regulation?

                  Thanks!
                  Last edited by Securitybyte; 5 March 2016, 02:51 PM.

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