Installing Evohome

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  • garmcqui
    Automated Home Guru
    • Jan 2015
    • 119

    Installing Evohome

    Ok so after taking some of the excellent advice on this forum, I've ordered an Evohome base kit, hot water kit and 8 TRVs, which I intend to install this weekend.

    At the moment, all radiators in the house are fitted with manual TRVs except the two in the hall, which just have normal valves. Now I understand the purpose of this, so the pump will never be pumping against a sealed circuit.

    However, if using the Evohome TRV's then could these radiators be fitted with Evohome TRVs too? I mean, would there ever be a time when the boiler/pump would be running against a sealed system?

    Thanks
  • HenGus
    Automated Home Legend
    • May 2014
    • 1001

    #2
    Hi. I am no plumber but I have an Evohome system. All my radiators have HR92s. My understanding, from 3 installers, is that a by-pass is required for pump run on when all the TRVs are closed. Unlike conventional TRVs, HR92s shut off completely when the temperature is reached. I have a bypass around my pump.

    Comment

    • roydonaldson
      Automated Home Guru
      • Jan 2013
      • 205

      #3
      But, I thought that unlike a traditional system, where the TRV's could be shut and the boiler still running, EvoHome will only be calling for heat via the Boiler Relay if it requires demand from an open HR TRV somewhere.

      I currently have a S Plan Plus layout and am trying to work out if I need to alter my 2 radiators in my downstairs and upstairs hallways to have TRV's on them, as they are just on normal valves today.

      Comment

      • roydonaldson
        Automated Home Guru
        • Jan 2013
        • 205

        #5
        It implies that you can have TRV's on all radiators provided you have an automatic bypass valve installed.

        Comment

        • SensibleHeatUK
          Moderator
          • Feb 2009
          • 228

          #6
          If you have a modern boiler that needs a pump run-on after all demand ceases (to dissipate the excess heat from the heat exchanger) then you need an automatic bypass whatever controls you use, fitted between the boiler and the zone valves, as it need to maintain flow through the boiler when the zone valves are closed. In this case bypass radiators are of no benefit as they are on the wrong side the the zone valve. Bypass radiators are used to maintain boiler minimum flow rates on systems that do not use pump run-on, and are there to ensure that if all the TRVs are closed then water can still flow. An automatic bypass negates the need for a bypass radiator, so it would not be needed on a modern system installation.

          You may still need a bypass radiator or automatic bypass when using Evo as the controls will create a boiler demand even if only one HR92 is partially open (the HR92 valve position modulates at low demand, when close to setpoint, to maintain accurate room temperature control), and this may not be enough to provide the minimum flow rate at the boiler.
          Sensible Heat
          SensibleHeat.co.uk

          Comment

          • garmcqui
            Automated Home Guru
            • Jan 2015
            • 119

            #7
            Ok so our house was only built in April, and the CH pump does indeed run on after any demand for heat. So in theory I should have a bypass already fitted?

            This is the layout of the plumbing around our unvented cylinder (there is solar heating too, hence all the extra pipes). I've tried to mark on what I think are the correct directions of relevant flow etc using the cylinder manufacturer's manual.

            IMG_5989.jpg Untitled.jpg

            Does it look like there is already a bypass fitted, and so I'd be ok to put HR92's on all my radiators?

            Currently the radiators in the hall upstairs and downstairs don't have TRV's, wheras all others do.

            Thanks
            Last edited by garmcqui; 8 January 2015, 02:29 PM.

            Comment

            • SensibleHeatUK
              Moderator
              • Feb 2009
              • 228

              #8
              I cannot see a bypass there, but it may be next to the boiler rather than in the cylinder cupboard. It sounds to me like the installer has not fitted TRVs in the two areas because that is probably where the basic room stats have been fitted and so removes the risk of the room stat being turned up and the TRVs turned down which would stop the heating from being controlled properly. In that case I can see no reason not to fit TRVs if/when you upgrade to Evo for full room zone control.
              Sensible Heat
              SensibleHeat.co.uk

              Comment

              • garmcqui
                Automated Home Guru
                • Jan 2015
                • 119

                #9
                Thanks for your reply.

                If no bypass there, I'm confused as to why there is both a return from the boiler and a return from the radiators?

                Checking if the bypass is beside the boiler will be a right pain, as all the pipework is fully boxed in round the boiler and none is visible.

                This is a screenshot of the Range manual:

                Untitled.jpg


                If all three zone valves are closed, yet the pump is still on overrun, then as far as I can see the only path for the water to take is the one I've highlighted in red below:

                IMG_5988.jpg


                Or have I completely misunderstood?

                Thanks
                Last edited by garmcqui; 8 January 2015, 02:52 PM.

                Comment

                • G4RHL
                  Automated Home Legend
                  • Jan 2015
                  • 1580

                  #10
                  My boiler is 17 years old, as is the house. There were TRVs fitted to every radiator except two as standard when we bought. Of the two one is the small downstairs cloak room and the other in the utility room. As the latter is in the same place as the boiler the radiator has never been used and is always off. The one in the cloak room though has been left without a TRV presumably because of the over run if all is hot and the heating goes off. Until I installed Evohome it was a regular occurrence to hear the pump still running for some time after the designated off time, often it could be 15 minutes. Since installing Evohome I don't think I have noticed the over run at all. It may not be happening now or perhaps not as much with Evohome using its brains to know more accurately when heat may be needed. The advice always given to me in the past by several central heating installers was never to put a TRV on at least one radiator.

                  As for having a thermostat in a room with TRVs it took me ages to convince my wife that if she adjusts that stat or puts the gas fire on, the rest of the heating around the house goes off! Not now though. The lounge is simply one zone. She can have the room as hot as she wants - but then I start stripping off or leave the room for cooler regions!!

                  Comment

                  • SensibleHeatUK
                    Moderator
                    • Feb 2009
                    • 228

                    #11
                    The bypass would be in the primary flow and return to the boiler, so more likely to be at the boiler end than at the cylinder. Your cylinder looks like a pre-plumed/wired package that avoids the need for the plumber to deal with this element. Depending on the boiler it may even have an internal bypass and pump within the boiler case. However if the ssystem is working properly now then as I said, the lack of TRVs ghas no bearing on whether there should be a bypass or not as the radiators are closed off from the boiler when their respective zone valves are closed, so play no part in maintain the water flow during any pump run on.
                    Sensible Heat
                    SensibleHeat.co.uk

                    Comment

                    • garmcqui
                      Automated Home Guru
                      • Jan 2015
                      • 119

                      #12
                      Ok, I understand now - thank you SensibleHeat!

                      Also, I think I *might* have found the bypass valve - it is in the airing cupboard (if it is what I think it is!!):

                      IMG_6021.jpg IMG_6018.jpg IMG_6019.jpg

                      Or am I wrong and it's something else entirely?

                      Thanks

                      Comment

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