increasing thermal capacity of ABV loop with small rad

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • sandyman
    Automated Home Sr Member
    • Mar 2016
    • 85

    increasing thermal capacity of ABV loop with small rad

    hi
    I have evohome with opentherm controlling viessman 100wb1b heat-only boiler. switched live output of evohome hot water kit BDR is also connected to the hot water "go hot now" input on the boiler, this makes the boiler run at 77 in order to re-heat the cylinder (which works great now).All rads have HR92's, and there is an ABV in the system.

    Once thing I have noticed in the warmer weather now (all CH off), is that in DHW demand times, just after the boiler has finished reheating the cylinder (which takes about 15 mins for a 10 degree recovery, I have offset of 10 degrees set), it then overruns (pump on, burner off) for about 30 mins.the pump is controlled by the boiler directly not evohome (has to be with opentherm IFAIU). I presume this is the boiler heat exchanger protection kicking in and keeping the pump on. After finishing heating the cylinder the flow temp will be about 80, watching the temp dial on the boiler it then climbs to about 90 just after the cylinder demand has shut down, then slow cools to 75 ish over the 30 minutes of overrun, then the overrun stops. During this overrun period the ABV has opened and the water is definitely going round the ABV's loop (I can feel the high temp in it). there is an overrun time parameter in the evohome hot water settings as well this is set to 0 mins in my case, it doesn't appear to have any effect in my system.

    The loop of pipe that is purely used by the bypass is pretty short (in the airing cupboard ) - about 50 cm at most. total amount of uninsulated primary pipe in the airing cupboard that it passes through maybe 1.5 metres including zone valves , pump etc. there than another 5m or so of Uninsulated under floor primary pipe, and then another 7m or so of Insulated (through a loft), comprising the rest of the primary circuit back to the boiler. whole thing times 2 flow for flow + return.

    I am thinking there isn't enough uninsulated capacity in the bypass loop to shed the heat quickly enough in this situation, hence the overrun lasting 30 mins.
    I suspect this is only happening in the summer when DHW demand is running the boiler in "very hot" mode. in the winter , the remains of the very hot water from DHW mode will be consumed by the CH demand, and/or if its goes into bypass after CH demand has finished, the temps at that point will be a lot lower so the overrun time needed a lot shorter.

    So.. wondering if I need to make the ABV bypass loop uninsulated part longer , by putting an extra tiny rad , in series with the ABV, in order to throw the heat away more quickly when DHW heatup has finished? Possibly with some diverting/isolating valves so that I can move it into the loop in summer and out of the loop in winter when its probably not needed? the small rad would go in the airing cupboard near to our clothes airer so heat would not be totally wasted.

    thoughts?
  • paulockenden
    Automated Home Legend
    • Apr 2015
    • 1719

    #2
    Shame about the wasted heat. If you opened up the over-run parameter in Evohome wouldn't it leave the DHW valve open during the over-run period, so at least the heat would be (over) heating the water, rather than just going round the bypass loop? Or have I misunderstood what that parameter does? You may even be able to set your target temp lower to allow for this additional heating during the over-run period.

    Or was it you who said you'd bodged (sorry, 're-engineered') the boiler connections so that theDHW valve also fires the boiler full blast? In which case the over-run parameter will no longer work.

    P.
    Last edited by paulockenden; 21 June 2016, 04:17 PM.

    Comment

    • sandyman
      Automated Home Sr Member
      • Mar 2016
      • 85

      #3
      Originally posted by paulockenden View Post
      Shame about the wasted heat. If you opened up the over-run parameter in Evohome wouldn't it leave the DHW valve open during the over-run period, so at least the heat would be (over) heating the water, rather than just going round the bypass loop? Or have I misunderstood what that parameter does? You may even be able to set your target temp lower to allow for this additional heating during the over-run period.

      Or was it you who said you'd bodged (sorry, 're-engineered') the boiler connections so that the CH valve also fires the boiler full blast? In which case the over-run parameter will no longer work.

      P.
      bodged not the best word (it was recommended, once I got to the right people), the DHW BDR ON state fires the boiler full blast on my setup. which works a treat (to achieve cylinder temp in double-quick time). The evo hot water overrun parameter is a mystery to me , doesn't seem to do anything. As you say if I could leave the pump on and zone valve to the hw open for another 5 minutes or so, after telling the boiler burner to turn off, it would probably dump all the remaining primary loop's useful heat into the cylinder and not need to run in bypass for so long. I have "played" with this parameter and it doesn't appear to do much that I can observe. perhaps with the controls now being evo-> opentherm -> boiler and boiler-> pump, it doesn't have any effect any more. hoping one of the honeywell bods on here can confirm/deny exactly what/how it is supposed to work.

      Ian

      Comment

      • paulockenden
        Automated Home Legend
        • Apr 2015
        • 1719

        #4
        See this from Top Brake: http://www.wordpress-1219309-4387497...ll=1#post21286

        So as I understand it, the boiler relay (or indeed OpenTherm Bridge) would shut off the boiler, but the DHW valve would remain open for the specified number of minutes. So the 'loop' would include the cylinder, rather than just the ABV, while the boiler was in bypass mode.

        But in your situation I think using the parameter would just keep the boiler firing for longer than you need (the system would think it's now off, but your not-a-bodge would keep it fired during the over-run period).

        P.
        Last edited by paulockenden; 21 June 2016, 04:29 PM.

        Comment

        • sandyman
          Automated Home Sr Member
          • Mar 2016
          • 85

          #5
          Originally posted by paulockenden View Post
          See this from Top Brake: http://www.wordpress-1219309-4387497...ll=1#post21286

          So as I understand it, the boiler relay (or indeed OpenTherm Bridge) would shut off the boiler, but the DHW valve would remain open for the specified number of minutes. So the 'loop' would include the cylinder, rather than just the ABV, while the boiler was in bypass mode.

          But in your situation I think using the parameter would just keep the boiler firing for longer than you need (the system would think it's now off, but your not-a-bodge would keep it fired during the over-run period).

          P.
          yeah, I read that one already but doesn't quite give me the answer. figure 4 is similar to my setup, substitute opentherm for the boiler BDR91, however what that diagram doesn't show is what goes on in the junction box i.e. is it the DHW bdr or the boiler that controls pump.

          actually not sure what my boiler does if the DHW "turbo mode" kit input is "on" but opentherm is saying "no demand". will try to test...

          Comment

          • paulockenden
            Automated Home Legend
            • Apr 2015
            • 1719

            #6
            Originally posted by sandyman View Post
            actually not sure what my boiler does if the DHW "turbo mode" kit input is "on" but opentherm is saying "no demand". will try to test...
            I assumed that the boiler would still run full-blast.

            If not, I think the over-run parameter should work as intended.

            P.

            Comment

            • sandyman
              Automated Home Sr Member
              • Mar 2016
              • 85

              #7
              Originally posted by paulockenden View Post
              I assumed that the boiler would still run full-blast.

              If not, I think the over-run parameter should work as intended.

              P.
              tested it, in my config it runs it at full blast for the length of time specified, because holding the DHW BDR + zone valve open, holds that input to the boiler high. I ended up with a boiler overheat protection kicking in! whilst trying to cool this down I stumbled on the ideal solution, don't need extra rads, just need to use the one I've got:

              boiler saying "I'm too hot (F2)", the pump was on , ABV open, all zones off. I manually opened a bathroom towel rail rad (take HR92 off, opened the wheel), dumped all the heat into that rad, job done. Even used the heat to dry the towels! for this to work automatically, need a way to designate a rad in Evo as a "dump rad" - i.e. if the DHW has just finished, and there is no CH demand, then open this rad fully (but do not call for heat). I can workaround this manually as of now - as I know the system is in "summer mode" with no CH demand, I can leave the HR92 off that rad and the wheel open, and in so doing expect I will get much quicker cool down and get some use out of that heat - but it would be nice to have feature for evo could do it automatically.

              that said, not sure if we are even getting the most basic features we all want like "which Hr92 is calling for heat" - which I desperately want as well. In one case I had the system running in late at night and I couldn't trace it , until I found an HR92 that had gone into "frost protection" mode. needless to say there was no frost in the house, must have been a bug, batteries out and back in that HR92 and job done. If I had had an indicator on the evo console which hr92 was calling, it would have made it a lot easier to find.

              Comment

              • DBMandrake
                Automated Home Legend
                • Sep 2014
                • 2361

                #8
                I have a suggestion for you that will probably work, provided that you aren't relying on the relay contact on the hot water zone valve to fire your boiler. Get yourself one of these timers for about £25:

                Contact us today for your free 242 page catalogue packed full of the latest branded products


                Spec sheet:



                I use one as a retrofit pump overrun timer on my system, however what I am suggesting is to use the timer to control your hot water zone valve.

                Disconnect the live supply wire to the hot water zone valve motor and connect it to the "line out" of the timer, and connect the trigger input of the timer to the BDR91 that was previously supplying the hot water zone valve, and which still supplies the "boiler high demand" input on your boiler. Obviously N and and L should be connected to Neutral and Live supply in your wiring centre. (The live supply should be a "permanent" supply - the same one as the permanent live to the BDR91's)

                Configure the dip switches on the timer to put it in "Resetting" mode and set it to about 5 minutes to begin with. (Which is done with some of the dip switches and a potentiometer wheel)

                Now what will happen is that when the hot water BDR91 turns on the zone valve will open immediately, however when the hot water BDR91 goes back off the boiler "high demand" that is boosting your flow temp will stop immediately, and the boiler will also go completely off if there is no central heating demand, however the hot water zone valve will remain open for the number of minutes set on the timer before closing.

                This means during at least some of your pump overrun period after hot water demand has ceased the hot water zone valve will remain open. This should give time for the excess heat in the boiler heat exchanger to be transferred to the hot water cylinder (using the hot water cyclinder's thermal mass as a heat-sink) causing the heat exchanger to cool down and prevent it overshooting 80 degrees.

                The advantage of doing it this way instead of adding deliberate heat loss to the ABV loop (something I've thought about doing before but decided against) is that no energy is wasted - the excess heat goes into the hot water cylinder.

                Finding the optimal time delay might take a little experimentation - too short and the heat exchanger won't be cooled enough before the zone valve closes, too long a delay and it will cause the hot water temperature to get too high - after all the Evohome unit has probably turned the hot water BDR91 off because the hot water has reached the desired temperature - if the zone valve stays open too long and the boiler is still running for central heating demand it might cause the hot water temperature to overshoot the target, but my guess is if you get the time set right you can prevent your boiler overheating and maybe overshoot the hot water target by only 1 or 2 degrees. (In which case you could just set your target hot water temperature slightly lower)

                I would set the timer to the minimum time required to keep the boiler's temperature under control when hot water demand turns off. You'll probably find you don't need a full 5 minutes, 2-3 minutes may be sufficient.
                Last edited by DBMandrake; 24 June 2016, 01:15 PM.

                Comment

                • sandyman
                  Automated Home Sr Member
                  • Mar 2016
                  • 85

                  #9
                  awesome idea, makes perfect sense - achieving the same end as evo's hot water overrun that they deliver if your system is laid out the way that they require, but by separating the "on" state of the bdr and the "on" state of the zone valve with this timer, should be able to make it work for me.
                  not sure if boiler "go hot" signal is currently coming from the zone valve's switched output or the BDR (they are logically the same at the moment) but I can always move it if its on the wrong one. Doesn't matter if the cylinder gets too hot in my case - its a pandora heat bank, its quite happy up to 80, so heating it more just means we have more stored hot water and so more time before the next recharge. as you say I can always play with the target temp. I turn that down in summer anyway, to give my solar thermal room to work.

                  I might even think about using two of these timers (although wired to different terminals) using a push button option for the other. Once thing we've lost with evo that SWMBO particularly doesn't like, is that with the old DHW timer (which was in the airing cupboard) if there was a need for a shower at an unusual time of day (when the timer was off) and not sure if enough hot water in the cylinder, just press the "+1 hr" button on that timer as you head for the bathroom and you know it will fire if it needs to so you don't get that dreaded mid-shampoo-goes-cold problem, which if you are SWMBO with long hair can be a serious situation!!! . So replicating that old +1hr button with a mechanical would be great also.

                  cheers
                  Ian
                  Last edited by sandyman; 24 June 2016, 02:55 PM.

                  Comment

                  • DBMandrake
                    Automated Home Legend
                    • Sep 2014
                    • 2361

                    #10
                    Originally posted by sandyman View Post
                    awesome idea, makes perfect sense - achieving the same end as evo's hot water overrun that they deliver if your system is laid out the way that they require, but by separating the "on" state of the bdr and the "on" state of the zone valve with this timer, should be able to make it work for me.
                    not sure if boiler "go hot" signal is currently coming from the zone valve's switched output or the BDR (they are logically the same at the moment) but I can always move it if its on the wrong one.
                    Yep - just move the "go hot" signal to being directly supplied by the hot water BDR91 if it isn't already.
                    Doesn't matter if the cylinder gets too hot in my case - its a pandora heat bank, its quite happy up to 80, so heating it more just means we have more stored hot water and so more time before the next recharge. as you say I can always play with the target temp. I turn that down in summer anyway, to give my solar thermal room to work.
                    I don't think hot water temperature would overshoot much anyway - because at the very least when the hot water BDR91 turns off the "go hot" signal would drop immediately causing the flow temperature of the boiler to throttle back to that demanded by central heating - which must be less than your "go hot" temperature otherwise you wouldn't have needed that in the first place. And in the no central heating situation like you have now the boiler would stop firing altogether.

                    The thermal mass of the heat exchanger whilst large compared to the water in the bypass loop (thus causing it to overshoot to 90) will be small compared to the mass of water in even a modest size hot water cylinder, so I think a few minutes of continuing to circulate the water through the hot water cylinder should be enough to bring the heat exchanger mass down to the water temperature and prevent it overshooting without a significant rise in hot water temperature.
                    I might even think about using two of these timers although wired to different terminals) using a push button option for the other. Once thing we've lost with evo that SWMBO particularly doesn't like, is that with the old DHW timer (which was in the airing cupboard) if there was a need for a shower at an unusual time of day (when the timer was off) and not sure if enough hot water in the cylinder, just press the "+1 hr" button on that timer as you head for the bathroom and you know it will fire if it needs to so you don't get that dreaded mid-shampoo-goes-cold problem, which if you are SWMBO with long hair can be a serious situation!!! . So replicating that old +1hr button with a mechanical would be great also.
                    Hmm, does the Evohome not have a manual override for hot water like it does for zone temperatures ? I don't have the hot water kit yet and am undecided whether I need it in my configuration, but I had assumed that you could schedule a temporary override ?

                    I should be clear that the timer I used is the MRT16-REM which is the version without any buttons. If you were wanting a second one for a +1 timer you'd need one of the other three types with a button/pull cord, and you'd probably want to configure it in on/off mode.

                    Where would you connect it though ? If you connected it in parallel with the hot water BDR91 then it would bring on your boiler and zone valve and heat the water, however you would not have any temperature regulation as now the Evohome is unable to control the hot water temperature. Remember that the hot water BDR91 doesn't just control scheduling of the hot water it also controls the temperature by turning off when the water is up to temperature.

                    So if you wired a separate timer in parallel with this it would keep heating up until your safety cutout triggered, which would potentially be quite a bit hotter than the temperature you have configured in the Evohome. If you have a backup conventional cylinder thermostat that was set only a little bit higher than the Evohome's temperature you could probably get away with it though, it would just mean that your +1 hour boost mode would be a little hotter than normal.
                    Last edited by DBMandrake; 24 June 2016, 03:09 PM.

                    Comment

                    • sandyman
                      Automated Home Sr Member
                      • Mar 2016
                      • 85

                      #11
                      Originally posted by DBMandrake View Post

                      Hmm, does the Evohome not have a manual override for hot water like it does for zone temperatures ? I don't have the hot water kit yet and am undecided whether I need it in my configuration, but I had assumed that you could schedule a temporary override ?

                      So if you wired a separate timer in parallel with this it would keep heating up until your safety cutout triggered, which would potentially be quite a bit hotter than the temperature you have configured in the Evohome. If you have a backup conventional cylinder thermostat that was set only a little bit higher than the Evohome's temperature you could probably get away with it though, it would just mean that your +1 hour boost mode would be a little hotter than normal.
                      evo does have override for hotwater, but its about 10 button presses. touch1 to wake up, touch2 hot water button to open the hw menu, touch3 on the current state (change off to on), touch 4 on the next switching on off time, touch lots of times on the up/down arrow to bring it forward to the time you want (however you want the hw on for), touch 10+ on the tick...if there was a quick mode "hw on for another 1/2hr" shortcut it would help.
                      Also course have to go to your controller, which in my case is in the hall, whereas in my house, as I suspect in many , the cylinder is not far from the bathroom, so a switch you can press near to the cylinder for "more hot water" is ergonomically nicer.

                      yes good point on the never-stop situation if I added a mechanical for the +1hr - it needs a cut out based on the temperature otherwise it would never stop. started to think it through and got to the same point myself.

                      Comment

                      • sandyman
                        Automated Home Sr Member
                        • Mar 2016
                        • 85

                        #12
                        Originally posted by DBMandrake View Post
                        I have a suggestion for you that will probably work, provided that you aren't relying on the relay contact on the hot water zone valve to fire your boiler. Get yourself one of these timers for about £25:

                        Contact us today for your free 242 page catalogue packed full of the latest branded products


                        Spec sheet:



                        I use one as a retrofit pump overrun timer on my system, however what I am suggesting is to use the timer to control your hot water zone valve.

                        Disconnect the live supply wire to the hot water zone valve motor and connect it to the "line out" of the timer, and connect the trigger input of the timer to the BDR91 that was previously supplying the hot water zone valve, and which still supplies the "boiler high demand" input on your boiler. Obviously N and and L should be connected to Neutral and Live supply in your wiring centre. (The live supply should be a "permanent" supply - the same one as the permanent live to the BDR91's)

                        Configure the dip switches on the timer to put it in "Resetting" mode and set it to about 5 minutes to begin with. (Which is done with some of the dip switches and a potentiometer wheel)

                        Now what will happen is that when the hot water BDR91 turns on the zone valve will open immediately, however when the hot water BDR91 goes back off the boiler "high demand" that is boosting your flow temp will stop immediately, and the boiler will also go completely off if there is no central heating demand, however the hot water zone valve will remain open for the number of minutes set on the timer before closing.

                        I would set the timer to the minimum time required to keep the boiler's temperature under control when hot water demand turns off. You'll probably find you don't need a full 5 minutes, 2-3 minutes may be sufficient.
                        I implemented this over the weekend , works a treat. I have

                        DHW demand BDR91 "B" terminal -> Boiler "turbo" DHW input + trigger input of MRT16
                        switched output of MRT16 -> H/w Zone valve input
                        h/w zone valve switched output -> CH pump switched live

                        now when the dhw demand bdr switches off , the MRT16 holds the h/w zone valve open and the pump runs on, for the duration of the MRT16's time.
                        the additional link from the h/w zone valve switched out to the CH pump was necessary because otherwise the boiler would wait until it felt it was too hot to put the pump on - which could be more than 5 mins - and then it would only run for a very short burst, then wait and do it again.

                        I'm playing with overrun times in the 2-3 minute bracket at the moment, seems to be cooling the boiler down to 60 or so nicely, and I gain another 1 or 2 degrees of cylinder temp.

                        buy you a virtual beer?

                        Comment

                        • DBMandrake
                          Automated Home Legend
                          • Sep 2014
                          • 2361

                          #13
                          Originally posted by sandyman View Post
                          I implemented this over the weekend , works a treat. I have

                          DHW demand BDR91 "B" terminal -> Boiler "turbo" DHW input + trigger input of MRT16
                          switched output of MRT16 -> H/w Zone valve input
                          h/w zone valve switched output -> CH pump switched live

                          now when the dhw demand bdr switches off , the MRT16 holds the h/w zone valve open and the pump runs on, for the duration of the MRT16's time.
                          the additional link from the h/w zone valve switched out to the CH pump was necessary because otherwise the boiler would wait until it felt it was too hot to put the pump on - which could be more than 5 mins - and then it would only run for a very short burst, then wait and do it again.
                          Glad to hear its working.

                          I'm a little bit confused though because in your original post you said that after the HW BDR91 turned off the pump was continuing to run (through the bypass loop) continuously for 30 minutes until the control of the boiler, presumably due to the boilers temperature based pump overrun:
                          Once thing I have noticed in the warmer weather now (all CH off), is that in DHW demand times, just after the boiler has finished reheating the cylinder (which takes about 15 mins for a 10 degree recovery, I have offset of 10 degrees set), it then overruns (pump on, burner off) for about 30 mins.the pump is controlled by the boiler directly not evohome (has to be with opentherm IFAIU).
                          Do you definitely have your bathroom bypass radiator turned back off again and have central heating turned off when testing the hot water overrun ? If so I'm not sure I understand why the pump would now be stopping immediately (without your extra pump connection) when it wasn't before.

                          In any case what you've done by wiring the zone valve switched output as an additional pump supply (in parallel with the boiler's own supply to the pump) is an excellent idea, and the correct way to wire it. You couldn't have wired the pump directly to the output of the MRT timer or the hot water valve would open for central heating too. The zone valve switched output has the necessary isolation for this to work.

                          I'm playing with overrun times in the 2-3 minute bracket at the moment, seems to be cooling the boiler down to 60 or so nicely, and I gain another 1 or 2 degrees of cylinder temp.
                          Excellent. So I guess the root cause of your problem was that the "go hot now" input of your boiler both raises the flow temperature setting and fires the boiler, when you really only wanted it to raise the flow temperature but not fire it. If it only raised the flow temperature of an already fired boiler but didn't fire the boiler itself (leaving that for the boiler relay or opentherm bridge) you could have used the hot water overrun setting in the Evotouch to give you your post hot water heating circulation time.

                          But because the hot water relay will also fire the boiler the way you had it wired before the hot water overrun setting in the Evotouch can't work and would only cause your hotwater temperature to overshoot without solving the overheating issue. (And so should be set to zero minutes to minimise any temperature overshoot of the hot water)

                          In any case it looks like you've found a satisfactory workaround - I think with some systems depending on their complexity and the specifics of the boiler etc it can be necessary to use some simple "building blocks" like external relays or timers to get the job done 100%.
                          Last edited by DBMandrake; 4 July 2016, 06:33 PM.

                          Comment

                          • sandyman
                            Automated Home Sr Member
                            • Mar 2016
                            • 85

                            #14
                            Originally posted by DBMandrake View Post
                            Glad to hear its working.

                            I'm a little bit confused though because in your original post you said that after the HW BDR91 turned off the pump was continuing to run (through the bypass loop) continuously for 30 minutes until the control of the boiler, presumably due to the boilers temperature based pump overrun:

                            Do you definitely have your bathroom bypass radiator turned back off again and have central heating turned off when testing the hot water overrun ? If so I'm not sure I understand why the pump would now be stopping immediately (without your extra pump connection) when it wasn't before.
                            Yes, the bathroom rad is off, all rads are off. what happened before (should have been more specific) was that when the dhw zone demand stopped the boiler would be at about 79. Over the next 5-10 mins the boiler displayed temp would slowly climb (with burner and pump off) due to residual heat. once it hit 85, the boiler would switch the pump on. temp would them climb more (I saw 95 once) then slowly start coming down over 30 mins. All this time pump on, water going to through ABV loop (which doesn't have much heat loss) as per my original thoughts.

                            Originally posted by DBMandrake View Post

                            In any case what you've done by wiring the zone valve switched output as an additional pump supply (in parallel with the boiler's own supply to the pump) is an excellent idea, and the correct way to wire it. You couldn't have wired the pump directly to the output of the MRT timer or the hot water valve would open for central heating too. The zone valve switched output has the necessary isolation for this to work.
                            yep, realised that one. I design networks for a living , this is just a different flavour


                            Originally posted by DBMandrake View Post

                            Excellent. So I guess the root cause of your problem was that the "go hot now" input of your boiler both raises the flow temperature setting and fires the boiler, when you really only wanted it to raise the flow temperature but not fire it. If it only raised the flow temperature of an already fired boiler but didn't fire the boiler itself (leaving that for the boiler relay or opentherm bridge) you could have used the hot water overrun setting in the Evotouch to give you your post hot water heating circulation time.
                            yes you would have hoped that the "hot" input would be ANDed with the boiler relay/OT bridge "on" input, but it seems to be OR'd.

                            Originally posted by DBMandrake View Post

                            But because the hot water relay will also fire the boiler the way you had it wired before the hot water overrun setting in the Evotouch can't work and would only cause your hotwater temperature to overshoot without solving the overheating issue. (And so should be set to zero minutes to minimise any temperature overshoot of the hot water)

                            In any case it looks like you've found a satisfactory workaround - I think with some systems depending on their complexity and the specifics of the boiler etc it can be necessary to use some simple "building blocks" like external relays or timers to get the job done 100%.
                            and some help from more than just the average heating installer... many thanks for this tip again
                            Ian

                            Comment

                            Working...
                            X