Switched to evohome & caused damage to boiler?

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  • zxdavb
    Automated Home Guru
    • Jan 2018
    • 106

    Switched to evohome & caused damage to boiler?

    I have recently switched all my TRVs to HR92s; I also swapped out my hive relay/controller for a BDR91 and it was easy as that - evohomed!

    FYI, I have a Worcester Greenstar 30si, and I have decommissioned a Hive system (with dumb TRVs) to install the above kit. But the main radiator (which was in the same room as the hive thermostat, and didn't have a TRV) was almost always on, as long as any one of the other radiators was on.

    So: I thought I was being clever by adding a TRV valve to the main radiator (I did this by simply de-pressurising the system using a bleed valve, using pipe-freezing spray, etc.).

    However, I started to think about it, and I got worried... What happens if all the TRVs are off (at 0%), and (due to sync delay) the boiler is still providing/pumping to the CH? Is it pumping against a closed system? If so, can I damage my system?

    For now, I have put a TRV on a small radiator at set it to 5/5... But do I need to call a plumber and put in some plumbing to cope with the above scenario?
  • chrisgare
    Automated Home Guru
    • Dec 2013
    • 182

    #2
    You need to have a bypass valve installed if you have HR92s on all the radiators. Do you have one?

    Comment

    • Dan_Robinson
      Automated Home Ninja
      • Jun 2012
      • 347

      #3
      Just leave the bathrooms uncontrolled.

      Or get a plumber in to fit an auto by-pass.
      Kind Regards - Dan Robinson (Jennings Heating Ltd)

      Comment

      • zxdavb
        Automated Home Guru
        • Jan 2018
        • 106

        #4
        Thanks for the advice.

        Originally posted by chrisgare View Post
        You need to have a bypass valve installed if you have HR92s on all the radiators. Do you have one?
        I thought so. I do not have a bypass valve installed (all I can see is a MagnaClean, and a silver cricket-ball-sized thing which I assume is some sort of expansion vessel).

        Originally posted by Dan_Robinson View Post
        Just leave the bathrooms uncontrolled. Or get a plumber in to fit an auto by-pass.
        For now, I've left a radiator in the main room uncontrolled. But I want to put in an external thermometer, so I may get both done, along with the upcoming service.

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          #5
          Some boilers have internal bypass valves too. So check that

          Comment

          • zxdavb
            Automated Home Guru
            • Jan 2018
            • 106

            #6
            Apparently, it has got one! I guess this is why I didn't do any (apparent) damage.

            However, the manual says: The boiler is equipped with an internal bypass. The internal bypass is not intended to be a substitute for an external system bypass. An external automatic bypass should be used if the system flow can be significantly adjusted or stopped by zone valves and thermostatic radiator valves (TRV).

            I guess it'll pay to have an automatic bypass fitted so I don't end up needing a new boiler?

            Comment

            • dty
              Automated Home Ninja
              • Aug 2016
              • 489

              #7
              Bear in mind that ABVs don't play well with pumps that adjust their pressure/flow rate based on the pressure in the system (proportional pumps).

              Comment

              • robj20
                Automated Home Sr Member
                • Aug 2017
                • 76

                #8
                IMO its better to have a bypass radiator.

                My system has an internal boiler bypass and an external auto-bypass, and still had issues. I now have the hall radiator as a bypass as well but low.

                The issue i found with an ABV was that when all radiators were off and the boiler still going for a short period the return temperature was no different to the flow temperature and the boiler didnt like this so shut down until a reset.
                I know have the bypass radiator so some heat can be dissipated the ABV still ensures a good flow but i use it mostly to keep the system quiet.

                Comment

                • Karrimor
                  Automated Home Jr Member
                  • Oct 2016
                  • 24

                  #9
                  What is exactly is a bypass radiator? And how do you go about setting up a radiator to act as a bypass radiator?

                  Comment

                  • dty
                    Automated Home Ninja
                    • Aug 2016
                    • 489

                    #10
                    Originally posted by Karrimor View Post
                    What is exactly is a bypass radiator? And how do you go about setting up a radiator to act as a bypass radiator?
                    It's a radiator without a thermostatic valve on it, so it's always open. I use my towel rails, and just leave the lockshields closed right down, but not fully down.

                    Comment

                    • paulockenden
                      Automated Home Legend
                      • Apr 2015
                      • 1719

                      #11
                      But note that if it's on your normal heating loop it'll only work as a bypass if:

                      a) all of the other rads have HR92s or whatever, and most importantly:

                      b) you don't have a CH valve, or else somehow (mechanically or electrically) you keep it open whenever the boiler is firing or over-running.

                      P.

                      Comment

                      • fergie
                        Automated Home Sr Member
                        • Mar 2017
                        • 92

                        #12
                        I'm the same as dty - I have 3 towel rails that are partly open plus an 'over run' in the garage which (usefully) heats a radiator there.

                        Comment

                        • IM35461
                          Automated Home Sr Member
                          • Jan 2012
                          • 69

                          #13
                          I have a similar boiler and the bathroom rad has no temperature regulation gadgets fitted so the boiler has always something to do.

                          Plus sometimes evohome can run your boiler in error and rather than just the boiler groaning in the middle of the night with the bypass valve open it can do something a little more useful and quiet.

                          Comment

                          • robj20
                            Automated Home Sr Member
                            • Aug 2017
                            • 76

                            #14
                            To think it could all be solved if you could set the hr92 to a minimum open level. Also a delay in switching radiator valves off so the boiler can do it's overrun. I would love to be able to set the hall and bathroom to a minimum of about 5% each.

                            Comment

                            • dty
                              Automated Home Ninja
                              • Aug 2016
                              • 489

                              #15
                              Originally posted by robj20 View Post
                              To think it could all be solved if you could set the hr92 to a minimum open level. Also a delay in switching radiator valves off so the boiler can do it's overrun. I would love to be able to set the hall and bathroom to a minimum of about 5% each.
                              The problem is that the HR92 has no practical way of knowing if a given valve position actually results in any flow or not. DBMandrake will be along shortly to explain his theories about the relationship between the HR92 reported valve position, the actual valve position, the deadbands at either end and how they relate to flow, and how the whole lot relates to boiler demand.

                              3... 2... 1...

                              Comment

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