Evohome Boiler Delta T Issue

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  • Evo
    Automated Home Lurker
    • Nov 2015
    • 8

    Evohome Boiler Delta T Issue

    Hi

    I installed the Evo home, 12 zones used on about 17 rads for a 4 bed house.

    I have a glow worm British Gas 330 condensing boiler with a Honeywell Bypass valve, within a few meters of the boiler.

    The boiler i have has it and it is 30 degrees, so if the boiler sees a difference between Flow and return of 30deg or more the boiler stops firing and the pump will just run.

    This is an issue for my house when i have rooms that are not used, set to 15degrees. With the recent cold snap we have had, this means that the boiler fires (to add a little heat in these room, or may have been firing for a higher temp room) and then not long after may pull through much cooler water form the radiators in the rooms that are not used. This then trips the boiler as a Delta T fault.

    I have a bypass, the bypass does trickle a flow of recirculated water to mix in with the cold and negate this issue. This does mean though that my system is less efficient at transferring hot water around the rest of the system.

    If I power down the boiler and then back up the fault is cleared and the boiler resumes.

    What practical uses does this feature have for the boiler?

    Why do some boilers have a Data T feature and some not?

    Can this temperature be adjusted?

    If i was to put an programmable open collector relay in series with the red light indicator, so that when the red light came on the relay would drop the feed to the boiler, then re-establish power this would reset the fault. Possible many other less desirable faults though.

    Any ideas?

    Thanks

    John

    PS Evo is a great system, i have many other questions that i will post concerning efficacy and boiler modulation later
  • paulockenden
    Automated Home Legend
    • Apr 2015
    • 1719

    #2
    Can you increase your pump speed? This will reduce the temperature differential across the boiler as the heat will be extracted faster.

    Comment

    • Evo
      Automated Home Lurker
      • Nov 2015
      • 8

      #3
      Originally posted by paulockenden View Post
      Can you increase your pump speed? This will reduce the temperature differential across the boiler as the heat will be extracted faster.
      Hi, pump is flat out. Plus i don't think a faster pump will help here, as it just means the colder water will get back to me all the quicker :-). Also remember the pump speed / ability to get water away or to the boiler is also governed by what is open or shut at the rad with the motorised rad valves. The issue occurs at night, when all temperatures are set to low, so the system is restricted in terms of water volume it can move. So again speeding the pump up i don't think could help. The issue has occurred in the day before, same situation. Very low ambient temperature in the house, apart form one room i was working in when i manually adjusted the temp in this room to make it more comfortable.

      Thanks for the thought though!

      John

      Comment

      • The EVOHOME Shop
        Site Sponsor
        • Dec 2014
        • 483

        #4
        I have never heard of this. I have read the manual on your Glowworm 330 boiler and there is no mention of the feature you mention. I suggest checking the heating thermistors and replacing if faulty (they should be 10K ohms at 25 degrees C). Bear in mind this boiler requires a minimum flow rate of 1289 litres/hr when range rated at 31kW, so make 100% sure the ABV is set correctly and the pump you have is not modulating.

        Comment

        • Evo
          Automated Home Lurker
          • Nov 2015
          • 8

          #5
          Originally posted by The EVOHOME Shop View Post
          I have never heard of this. I have read the manual on your Glowworm 330 boiler and there is no mention of the feature you mention. I suggest checking the heating thermistors and replacing if faulty (they should be 10K ohms at 25 degrees C). Bear in mind this boiler requires a minimum flow rate of 1289 litres/hr when range rated at 31kW, so make 100% sure the ABV is set correctly and the pump you have is not modulating.
          Hi. If you check the error code section near the back code 26 'maximum delta temp reached'. I also spoke to tech support. Agree about flow rate but this will vary depending on what evo has shut down. If I just have the bathroom towel going, the things will be restricted. But I know the error only occurs when it is pretty cold outside. E.g when measued temp at rad is down to 15 deg. We had the cold snap the other week, it happened then.

          ABV has to be over set to allow a trickle under normal use. Otherwise cold water coming back when boiler is delivering more than 30 deg difference will trip the delta fault. That's what made this happen again, I adjusted to see if I could reduce the trickle, and improve heat transfer when one rad only is running. The cold snap councindetally occurred one day after 😡 Reduced hot water trickle + lower ambient temp made it happen again.


          Cheers.

          John

          Comment

          • paulockenden
            Automated Home Legend
            • Apr 2015
            • 1719

            #6
            So your boiler craps out if it heats the water too well???? What kind of a design is that? Surely as long as the output temp isn't stupidly hot why does the delta temp matter? A big delta surely means that the boiler is working efficiently?

            Sounds daft! Anyone know the logic if tripping on a high (actually, not /that/ high) delta temp?

            P.

            Comment

            • Evo
              Automated Home Lurker
              • Nov 2015
              • 8

              #7
              Hi. Just had to slacken off the Bypass Valve again after it tripped again today :-(. I guess i will call Glow worm again and ask them if there is any update PCBs where the Dlta T does not switch of the boiler. Anyone have any explanation as to why having a temp greater than 30 degrees between Flow an returned at the boiler is such an issue?
              Cheers

              John

              Comment

              • The EVOHOME Shop
                Site Sponsor
                • Dec 2014
                • 483

                #8
                I suggest getting Glowworm out on their fixed fee to get this resolved. Normally condensing boilers want cold returns, but sometimes (on poorly produced boilers) cold returns can cause corrosion on the heat exchanger if it is too cold for too long (UFH systems for instance). Very strange, but true...

                Comment

                • Evo
                  Automated Home Lurker
                  • Nov 2015
                  • 8

                  #9
                  Hi

                  Unless they can make a change they will say as they have said before the boiler is behaving normally. The evo system is simply doing what it is supposed to and so is the boiler. Only way to resolve this is if they can adjust the time or the number of times delta t occurs to generate the delta t fault. I did not get chance to speak to them this week, will see next week if there is scope for adjustment on the board. I slackend the bypass a bit more, it has not gone since but as I say it makes for a less efficient heat transfer, so not ideal.

                  Thanks for your comments.

                  John
                  Last edited by Evo; 15 January 2016, 10:11 PM.

                  Comment

                  • paulockenden
                    Automated Home Legend
                    • Apr 2015
                    • 1719

                    #10
                    I'd suggest that a boiler which refuses to heat water more than 30 degrees is broken by design.

                    You could easily have a situation in a conventional (non-Evohome) home where only one TRV was open.

                    Comment

                    • Fursty Ferret
                      Automated Home Sr Member
                      • Oct 2014
                      • 84

                      #11
                      You really need a flow meter installed after the bypass valve so you can ensure that sufficient water is going through the boiler to satisfy the minimum requirement. "Slackening the valve" a bit is not the appropriate way to do this.

                      Comment

                      • Evo
                        Automated Home Lurker
                        • Nov 2015
                        • 8

                        #12
                        Hi

                        Flow will vary constantly depending upon what is open and how much. Flow meter will not help much. Ideally I should shut everything down, call for heat and wind back for flow on the bypass. This works for the shutdown side but not for mixing hot with colder return issue. For this its a bit trial and error. However, I agree it is not great, and it would be great if booker delta has to be done it should be modifiable to monitor for 30 degree delta over X time with time being varied with a pot on the PCB say. That would help me.

                        Re the 30degree from earlier post, this is a difference between flow and return on my boiler. This happens for me when cold water in a rad or rads (circa 15 degrees) is released and mixed into the return that may be running at 40 - 60 degree especially if a towel rail is the only thing running. Recall the boiler is running at say 69 on the flow. Then evo opens up a rad which contains water at say 15 degrees. This water cools down the return temp to a level that depends on ambient temp, how far away is is, volume of rad etc. If this drops the return to a delta of 30 or more the boiler trips and I have to power cycle to restart.

                        Cheers.

                        John

                        Comment

                        • The EVOHOME Shop
                          Site Sponsor
                          • Dec 2014
                          • 483

                          #13
                          Originally posted by Evo View Post
                          If this drops the return to a delta of 30 or more the boiler trips and I have to power cycle to restart.
                          This is ridiculous... Change the boiler to Intergas which relishes good controls and cold return temps.

                          Comment

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