EvoHome Hot Water Kit >> Megaflow CL210

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  • omdaddi
    Automated Home Lurker
    • Nov 2018
    • 5

    EvoHome Hot Water Kit >> Megaflow CL210

    Hi, I am fairly competent DIYer, but the evoHome hot water kit slightly concerns me and I could do with a sanity check.

    Background:
    I have three heating circuits., When I updated the boiler a few years ago the plumber put in three BDR91s (in a row, 2cm apart) to control the circuits with remote thermostats. The BDR91s control the valve on each heating circuit. It took some fun and games before I worked out (RTM...) that my assumption that the controller just "needed to know" which BDR91 belonged to which zone was wrong. Eventually I put them all in binding mode and then they were all bound to the controller when setting up "Boiler Control". I expected them all to come on every time any room asks for heat, but weirdly they don't. But the ones coming on don't always match where the heat is required, although in the end the heat always arrives (e.g. circuit one is demanding heat now, and the BDR for circuit 1 and 3 are on, but circuit 2 is off). Thinking this was the nearness I have separated them by 30cm, but it has made no difference. I do wonder about binding them all to one BDR91, but, it works... so I will leave it as it is. The BDR91s have power all day now because I changed the timer controls to ON for those circuits. evoHome is in charge.

    Anyhow... I just purchased a hot water tank kit to fit to my Megaflow tank. Mine is a CL210. They are very much sealed but my model has an immersion heater half way up with a pocket for a thermostat. I intend to remove the thermostat and isolate it, then stick the remote sensor in to the pocket. I can refit the immersion heater thermostat if I want, though have only needed it once in 20 years, and that was when the boiler was replaced.

    I have talked through what to do about wiring with a friend who is a commercial heating engineer (not domestic), but wanted a sanity check, so if anyone sees this a metaphorical thumbs up would be appreciated. The guarantee on the Megaflow is 25 years and I don't want to interfere with it (though it is 20 years this year!).

    This is the plan:

    1. Isolate heating system from mains.
    2. Tap L and N from the junction box where all the other BDR91 come from and take to the L and N in the new BDR91. BDR91 will now be ready to rock and roll.
    3. Wire the A and B sockets in the BDR91 in SERIES with the ORANGE (or grey) wire to the inlet valve to the megaflow.
    4. Tweak up the Megaflow stat to higher than the set point on the evoHome (I have not taken the cover off the control point on the megaflow, it is in an unbelievably awkward position, it will be possible but I am not going near it until the power is off. I only want to do it once).
    5. Remove and isolate immersion thermostat, freeing up a void half way up the tank.
    6. Push remote probe in to the void, seal lead in with something sensible, I have a vast array of rubber grommets, one should be right.
    7. Connect probe to hot water unit, pair it all up with the controller...
    8. Power on.

    As I see this, the megaflow will always think the water is too cold, so will be powering the valve. The BDR91 will then have full control over whether the valve opens or closes. If the tank gets too hot, the megaflow will cut the power to the valve.

    I have not touched anything on the megaflow to do this, so I think the warranty will be fine. (If anything goes wrong and the BDR freezes open, the wiring is identical to what it was before), I will just get hotter water.

    Does this make sense??
  • mtmcgavock
    Automated Home Legend
    • Mar 2017
    • 507

    #2
    Originally posted by omdaddi View Post
    3. Wire the A and B sockets in the BDR91 in SERIES with the ORANGE (or grey) wire to the inlet valve to the megaflow.
    No this would be the brown wire to the Motorised valve you need to tap into. So L to A, B to MegaFlo Stat Common, MegaFlo Stat to Motorised Valve Brown. Essentially you replace what would have been your switch live from the clock with the BDR91. Don't mess with any Orange or Grey wires as these are just S/Ls for the boiler.
    Originally posted by omdaddi View Post
    4. Tweak up the Megaflo stat to higher than the set point on the evoHome (I have not taken the cover off the control point on the megaflow, it is in an unbelievably awkward position, it will be possible but I am not going near it until the power is off. I only want to do it once).
    Yes that's fine.

    Originally posted by omdaddi View Post
    5. Remove and isolate immersion thermostat, freeing up a void half way up the tank. - Wouldn't do this, the stat will be in the wrong place. Should be about 1/3 up from the bottom. Sounds like your MegaFlo is the same as mine, when you remove the cover for the wiring where the normal stat goes theres a pocket where the traditional probes are. You can fit in your EvoHome probe in there too. Will give better accuracy for HW readings.

    Comment

    • fezster
      Automated Home Sr Member
      • Dec 2017
      • 72

      #3
      Make sure the overheat stat on the megaflo still closes the Zone Valve when activated. This is a very important safety feature.

      Comment

      • paulockenden
        Automated Home Legend
        • Apr 2015
        • 1719

        #4
        I think there's a lot of scaremongering about Megaflow and other similar tanks.

        IF the tank was being heated by an immersion heater, and IF there wasn't a pressure relief valve then yes, it could become a big wet bomb.

        However.... When heated via a loop of water from your boiler it's never going to get over 80 degrees or so. The only risk is a slight one of scalding from any hot taps that take a direct feed.

        As for trying to fit the sensor in, the official Evohome sensor is quite bulky. But you can buy 10k NTC thermistors which are much smaller. I use one of these: https://www.ebay.co.uk/itm/122775246996 - works perfectly, and easy to slide into a pocket alongside any existing sensors.

        Comment

        • mtmcgavock
          Automated Home Legend
          • Mar 2017
          • 507

          #5
          Originally posted by paulockenden View Post
          I think there's a lot of scaremongering about Megaflow and other similar tanks.

          IF the tank was being heated by an immersion heater, and IF there wasn't a pressure relief valve then yes, it could become a big wet bomb.

          However.... When heated via a loop of water from your boiler it's never going to get over 80 degrees or so. The only risk is a slight one of scalding from any hot taps that take a direct feed.

          As for trying to fit the sensor in, the official Evohome sensor is quite bulky. But you can buy 10k NTC thermistors which are much smaller. I use one of these: https://www.ebay.co.uk/itm/122775246996 - works perfectly, and easy to slide into a pocket alongside any existing sensors.
          I've seen on 3 separate occasions where the high limit stat has kicked out (So 90oc) when other components have either failed, or been installed incorrectly when been heated by a boiler. It's there for a reason. Also removing it won't comply to any regs.

          Comment

          • Edinburgh2000
            Automated Home Guru
            • Dec 2016
            • 134

            #6
            Originally posted by paulockenden View Post
            However.... When heated via a loop of water from your boiler it's never going to get over 80 degrees or so. The only risk is a slight one of scalding from any hot taps that take a direct feed.
            I have a Megaflo 210 cylinder and it is pressure that bothers me much more than temperature. As I understand it, there is no physical diaphragm to separate the air bubble at the top of the cylinder from the water. So the air gradually dissolves into the water reducing the ability of the cylinder to act as an expansion vessel. This is different from the heating circuit on an unvented system, where we tend to use expansion cylinders with a physical diaphragm. I failed to top up the air in my Megaflo and found that the pressure in my domestic hot water plumbing had got close to the 8 bar of the cylinder's relief valve setting, without any failure on the part of a thermostat. This was just heating the cylinder from 5oC to 60oC. I found it hard to operate my kitchen hot tap when it had 8 bar behind it! I now make a routine of adding air into the cylinder, by running a bath tap, shutting the inlet valve to the cylinder and opening the relief valve to admit air. (The cylinder is at the top of the house.) I do this about once a month and it keeps the air sufficiently topped up to prevent significant over-pressure events.

            I don't mind doing this as I understand how all this works. I'm not sure my granny would be too keen on needing to top up the air in her hot water cylinder though, so it does seem a poor design.

            Comment

            • fezster
              Automated Home Sr Member
              • Dec 2017
              • 72

              #7
              I find my bubble needs recharging every 6m or so. I have a potable expansion vessel which I'll have installed at some point so I can do away with the megaflo's poor solution.

              Comment

              • mtmcgavock
                Automated Home Legend
                • Mar 2017
                • 507

                #8
                Originally posted by Edinburgh2000 View Post
                I have a Megaflo 210 cylinder and it is pressure that bothers me much more than temperature. As I understand it, there is no physical diaphragm to separate the air bubble at the top of the cylinder from the water. So the air gradually dissolves into the water reducing the ability of the cylinder to act as an expansion vessel. This is different from the heating circuit on an unvented system, where we tend to use expansion cylinders with a physical diaphragm. I failed to top up the air in my Megaflo and found that the pressure in my domestic hot water plumbing had got close to the 8 bar of the cylinder's relief valve setting, without any failure on the part of a thermostat. This was just heating the cylinder from 5oC to 60oC. I found it hard to operate my kitchen hot tap when it had 8 bar behind it! I now make a routine of adding air into the cylinder, by running a bath tap, shutting the inlet valve to the cylinder and opening the relief valve to admit air. (The cylinder is at the top of the house.) I do this about once a month and it keeps the air sufficiently topped up to prevent significant over-pressure events.

                I don't mind doing this as I understand how all this works. I'm not sure my granny would be too keen on needing to top up the air in her hot water cylinder though, so it does seem a poor design.
                Without going too off topic from the OP question....

                The MegaFlo has a baffle in the top of it along with the air bubble, i'm guessing that's what you mean. The issue is people don't realise/haven't been informed that the cylinders should be serviced annually and the internal or external expansions need to be checked and recharged annually along with the safety devices. They also don't seem to think that when they'e got water dripping from the discharge pipe that there is something wrong.

                To be honest the external expansions ones aren't much better, the still usually need recharging every 2-3 years and i've had a few vessels start leaking at 5 years old which isn't good.

                If you're topping up the air gap every month then you've got an issue, you need to have an external expansion fitted to the Cold inlet of the cylinder (After the pressure reducing and Non Return valve). This would prevent you having to do this so regularly. I wouldn't want to be over working the PRV on such a regular basis.

                I had one customer with a MegaFlo, 17 years old. He'd never recharged it and the air gap was still working as it should (Admittedly it maybe didn't much use)...I wouldn't of expected an External vessel to have lasted so long.

                Comment

                • omdaddi
                  Automated Home Lurker
                  • Nov 2018
                  • 5

                  #9
                  Originally posted by mtmcgavock View Post
                  No this would be the brown wire to the Motorised valve you need to tap into. So L to A, B to MegaFlo Stat Common, MegaFlo Stat to Motorised Valve Brown. Essentially you replace what would have been your switch live from the clock with the BDR91. Don't mess with any Orange or Grey wires as these are just S/Ls for the boiler.
                  I just checked this thread - found that the notification had gone in to spam folders.

                  I did all the wiring today, but had not seen your excellent reply. I did break in to with the orange wire, I was wondering why the water temperature was staying so constant. I am hoping effectively disconnecting it for 12 hours won't have broken anything.

                  What I have done now is simply put the BRD91 relay in series with the brown wire from the valve.

                  Originally posted by mtmcgavock View Post
                  So L to A, B to MegaFlo Stat Common, MegaFlo Stat to Motorised Valve Brown.
                  The junction box had two brown wires joined. I am hoping that one of these is the L you mention and one is the MegaFlo stat common. All I did was pull one brown wire, connect it up to A, then bring B down to where the brown wire used to be.

                  I have not yet looked at the MegaFlow settings at all. For historic and annoying reasons the access panel is about 150 degrees away from me, 20cm from a wall. It is very awkward. I have not looked at it. My cunning plan was to set the evoHome temp 1 degree below the temp that the MegaFLow holds it at (58 degrees) then use the run on setting on the evoHome, which I assume lets the heating overshoot for a few minutes. Assuming I do try and look at it tomorrow, I am hoping there is a big dial I can just twiddle up?

                  Originally posted by mtmcgavock View Post
                  Wouldn't do this, the stat will be in the wrong place. Should be about 1/3 up from the bottom. Sounds like your MegaFlo is the same as mine, when you remove the cover for the wiring where the normal stat goes theres a pocket where the traditional probes are. You can fit in your EvoHome probe in there too. Will give better accuracy for HW readings.
                  I will check this tomorrow, but as I say, the access is bloody difficult.

                  I am very grateful that you took the time to correct my error.
                  Last edited by omdaddi; 14 November 2018, 02:13 AM. Reason: Noticed the extra comment about the stat pocket!

                  Comment

                  • omdaddi
                    Automated Home Lurker
                    • Nov 2018
                    • 5

                    #10
                    Originally posted by fezster View Post
                    Make sure the overheat stat on the megaflo still closes the Zone Valve when activated. This is a very important safety feature.
                    How would I do this?

                    Thanks for taking the time to help me out.

                    (I am slowly working this out. Once I put the hot water relay in I realised I had made the (common) error of setting up the zone valves as boiler control. I have just set them up (I have three zones) by binding them at the same time when setting up the guided configuration. I worked out that there is < 10 litres in each circuit with all the TRVs closed downso am not going to worry too much.

                    All a bit of an adventure really, though not sure it is going to save money. The kids are delighted they can crank up the temperature in their rooms!

                    Comment

                    • fezster
                      Automated Home Sr Member
                      • Dec 2017
                      • 72

                      #11
                      Originally posted by omdaddi View Post
                      How would I do this?

                      Thanks for taking the time to help me out.

                      (I am slowly working this out. Once I put the hot water relay in I realised I had made the (common) error of setting up the zone valves as boiler control. I have just set them up (I have three zones) by binding them at the same time when setting up the guided configuration. I worked out that there is < 10 litres in each circuit with all the TRVs closed downso am not going to worry too much.

                      All a bit of an adventure really, though not sure it is going to save money. The kids are delighted they can crank up the temperature in their rooms!
                      Someone more experienced than me will be able to tell you for sure, but my understanding is the Megaflo temp stat has an overheat stat built into it (effectively wired in series). It has a reset button on the front if it activates. So, in theory, as long as the stat is wired in series between your BDR91 and your motorised valve, the valve should close when the stat (or the overheat stat) open.

                      This is a very important safety feature and actually illegal to work on if you're not G3 qualified. This is not to scare you, but rather to make apparent to you that if you do insist on DIY, make sure you are 110% confident in what you are doing.

                      Comment

                      • omdaddi
                        Automated Home Lurker
                        • Nov 2018
                        • 5

                        #12
                        I hear you. I have not done this lightly. In addition to my air con engineer friend, I figured that there were three wires I could have bridged, two would have worked, so I am 66% to start with. Then when I chose wrong, the water was clearly not working (the evoHome was not shutting off the heating, and the boiler was happily keeping the water at 68 degrees), I knew there was something wrong so I just unbound the BDR91 and left it on, and the circuit was back to before my fiddling.

                        Last night I read the post by mtmcgavock and realised my error with the orange wire. I immediately fixed it and the system immediately started working as expected. So I am 99.9% sure I am OK.

                        Today I looked at the control panel of the MegaFlow. It was awkward, facing away from me to around the left hand side of the cylinder with three pipes in front of it. Changing the temperature up was trivial (a dial as expected) but I could not see a pocket for the sensor. I figured that the control body was held in by the two screws either side of the cut out, and pretty much had to unscrew them with my fingers as there was barely enough room for the screwdriver to loosen them, plus the screws would be gone forever if I dropped them.

                        I very carefully moved the control body out, but since I couldn't see in very well I couldn't see the pocket for the probe as described by mtmcgavock at all. I persevered and could just see two black wires disappearing, which must have been the MegaFlow stat leads. I fetched a mirror and bingo - I could see a rectangular pocket in the bottom right hand corner of the cut-out - exactly where it was impossible for me to see without the mirror. I gently pushed the black leads aside and carefully pushed in the evoHome probe. If I had had full access I am confident I would not have needed to take out the control body. Putting the screws back in was exciting, but I managed no drops. I returned the immersion heater to its original position and now everything is working perfectly.

                        (I did have a little worry when the water was 48 degrees and no heating came on, but I worked out the hot water settings in the setup menu (System Devices > Stored Hot Water. The Stored Water Differential was 10 degrees and I had set the water to 57 to keep it below what I thought was the max on the MegaFlow before I went in to the MegaFlow panel to tweak up its stat.) It is now at 58 degrees. I am not worrying too much about Legionella. It was set at 58 degrees for the last 20 years.

                        As I type, the water has heated from 48 to 57 over the last hour or so, and I am resisting the urge to stand by the relay to watch it go off at 58 degrees. That is the last test.

                        Hope this helps someone.

                        Later: Well, it went off, but I never saw 58 on the display. I guess it was there for a very short time and is now slowly cooling down towards the differential.
                        Last edited by omdaddi; 14 November 2018, 03:30 PM. Reason: Update

                        Comment

                        • mtmcgavock
                          Automated Home Legend
                          • Mar 2017
                          • 507

                          #13
                          What I usually do is set the cylinder temperature control on maximum. On the MegaFlos this is 70oc where as others are usually 65oc. I then set the EvoHome to a more desirable temperature (55oc) and let the Evohome control the temperature. If Evohome failed to shut off the MegaFlo will shut down at 70oc then.

                          If you set the MegaFlo at a similar temperature to the EvoHome there's always the possibility that the MegaFlo stat will shut off first and then the BDR91 will stay open until a time period ends. Also if you are wanting to use the Over Run the Megaflo stat will have switched the zone valve off therefore making unable to overrun. I have mine set to 55oc and a 3 minute over run which usually increases the temperature to 57oc.

                          Comment

                          • omdaddi
                            Automated Home Lurker
                            • Nov 2018
                            • 5

                            #14
                            Yes, that was the plan, but I didn't set the MegaFlow until I knew everything was working. It is at 70°C now I think. (Though that is a guess of course, do you turn it clockwise or anticlockwise to turn it up? I guessed clockwise (remember, I couldn't really see it)).

                            It all seems to be working fine, but I just noticed that the water is at 61°C (set point is 59°C) but the evoHome is still happily keeping the thermostat on.

                            I have no boiler overrun and I checked the setpoint as 59°C just now. When I press the BRD91 button the valve closes and the boiler shuts off. I guess this proves I turned the Megaflow thermostat the right way!

                            I suspect that this is a communications issue. I absent mindedly put the sensor box pretty close to the BRD91 (it looked nice), but I just moved it, and hope this will solve the issue. This is the flaw in my keeping the three zone BRD91s in place. I now have five transmitters, all are 30cm+ from any other, but not much more than that. I don't know how to test the water without waiting for a long time, or setting a silly set point and changing the differential to zero.

                            My only other issue is with one of my zones, which continually tells me there is an actuator fault despite working. This has only one valve. I have swapped it for two other randoms in the house, but it keeps failing. I wonder if there is a phantom bind on it, but have deleted the zone a couple of times too.

                            Later: I did the silliy thing with the hot water set point and differential and the water switched on and off perfectly, so hopefully that is done! I remembered to turn it back
                            Last edited by omdaddi; 14 November 2018, 10:13 PM.

                            Comment

                            • jb80
                              Automated Home Jr Member
                              • Aug 2018
                              • 11

                              #15
                              Originally posted by omdaddi View Post
                              ... I couldn't see the pocket for the probe as described by mtmcgavock at all. I persevered and could just see two black wires disappearing, which must have been the MegaFlow stat leads. I fetched a mirror and bingo - I could see a rectangular pocket in the bottom right hand corner of the cut-out - exactly where it was impossible for me to see without the mirror. I gently pushed the black leads aside and carefully pushed in the evoHome probe.
                              So glad that I stumbled across this thread as I too have a Megaflow CL210 cyclinder with Evohome. I was initially stumped with how to install the Honeywell cyclinder temperate probe and this clue above solved it for me. I am enclosing a close-up photo of the cyclinder pocket with the black leads connected to the cut-out safety thermostat. Simply insert the Honeywell probe into the same pocket, it's just wide enough to accommodate both. The result works perfectly!

                              Wiring panel on Megaflow CL210 cyclinder

                              20190831_093026.jpg

                              Black leads connected to the cut-out safety thermostat

                              20190831_093035.jpg

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