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Thread: Evohome Opentherm Boiler decision and set up

  1. #101
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    Thanks Gus, Firstly apologies, I have just seen your PM from February explaining the same set up!

    I agree with what you say, it would make sense for the HW to get priority, for the CH to take over once HW is no longer needed. My only concern is that when my HW had a 1hr 30 time slot every second morning, during the 'morning heat up' - the water didn't get hot at all, i was constantly 'boosting' via the controller. since taking this slot an hour prior - all seems to be good.

    I'm also considering how this will all work with a UFH system - presume that the UFH would work in tandem with the CH given that the UFH valve will work independently.

  2. #102
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    Quote Originally Posted by 1animal1 View Post
    Thanks Gus, Firstly apologies, I have just seen your PM from February explaining the same set up!

    I agree with what you say, it would make sense for the HW to get priority, for the CH to take over once HW is no longer needed. My only concern is that when my HW had a 1hr 30 time slot every second morning, during the 'morning heat up' - the water didn't get hot at all, i was constantly 'boosting' via the controller. since taking this slot an hour prior - all seems to be good.

    I'm also considering how this will all work with a UFH system - presume that the UFH would work in tandem with the CH given that the UFH valve will work independently.
    Thinking about your problem a bit more, I recall having a lengthy conversation with my installer about the valve configuration needed to work with an Atag boiler. The Atag ONE controller only works on a modified ‘Y’ configuration: this was confirmed by Atag Support. Could this be your problem; that is, your HW valve is not triggering a HW boiler flow demand?

  3. #103
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    Quote Originally Posted by HenGus View Post
    Thinking about your problem a bit more, I recall having a lengthy conversation with my installer about the valve configuration needed to work with an Atag boiler. The Atag ONE controller only works on a modified ‘Y’ configuration: this was confirmed by Atag Support. Could this be your problem; that is, your HW valve is not triggering a HW boiler flow demand?
    Surely you wouldn't be using the Atag controller if you've got Evohome?

  4. #104
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    Quote Originally Posted by mtmcgavock View Post
    Surely you wouldn't be using the Atag controller if you've got Evohome?
    I have moved on from Atag/Evohome/OT. The Atag ONE controller uses the same Atag boiler EBUS as Evohome OT. The Atag ONE controller requires a 3 port diverter valve. The discussion that I had with my installer and Atag Support at the time was that a 3 port diverter valve was also needed for Evohome OT control on an IS boiler with an unvented cylinder. My installer’s compromise was a zone valve for HW, and an inline open valve for CH. The latter closed whenever the HW zone valve opened.

    What I am suggesting is that it is possible the ‘system’ as configured is missing the ‘trigger’ for the boiler to go to TMaxSet if all the zones are at their set temperatures when there is a HW reheating demand. All I can say is that my HW priority system worked well with Evohome OT.

    I may be well wide of the mark. My new home has an annoyingly noisy WB boiler with 2 simple TPI thermostats and TRVs. It’s one saving grace is that it appears to be a very efficient heating system with none of the complexity of Evohome.

  5. #105
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    Quote Originally Posted by HenGus View Post
    I have moved on from Atag/Evohome/OT. The Atag ONE controller uses the same Atag boiler EBUS as Evohome OT. The Atag ONE controller requires a 3 port diverter valve. The discussion that I had with my installer and Atag Support at the time was that a 3 port diverter valve was also needed for Evohome OT control on an IS boiler with an unvented cylinder. My installer’s compromise was a zone valve for HW, and an inline open valve for CH. The latter closed whenever the HW zone valve opened.

    What I am suggesting is that it is possible the ‘system’ as configured is missing the ‘trigger’ for the boiler to go to TMaxSet if all the zones are at their set temperatures when there is a HW reheating demand. All I can say is that my HW priority system worked well with Evohome OT.

    I may be well wide of the mark. My new home has an annoyingly noisy WB boiler with 2 simple TPI thermostats and TRVs. It’s one saving grace is that it appears to be a very efficient heating system with none of the complexity of Evohome.
    The only thing the diverter is doing is preventing the central heating being heated whilst there is a hot water demand. So by having what your installed fitted on your last system it's the same as a diverter. The 'trigger' or demand will come from the controller not the zone valve.

    I think the issue with 1animal1 is that the NO heating valve that has been fitted is not closing when there is a HW demand.

  6. #106
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    Evening chaps

    Gus, I can't see that this is anything to do with the Atag, the boiler is a slave to the Evo OT module which in turn is a slave to the Evo Controller - the system is a CH system primarily as per the Honeywell OT instructions, when HW is requested, power shuts the CH valve and opens the HW valve in tandem (which sounds exactly as yours was). The fact that the system is now working without issue, because it's programmed for the HW to not coincide with a high CH demand, suggests Evohome gives priority I would have thought, possibly delaying the HW triggering. Unless I'm misunderstanding what you are suggesting?

    Upon thinking further, the additional UFH system under a further normally closed valve would work independent of both the HW and CH, as this would run off the main 22mm branch from the boiler and not after the CH/HW valves - initially powering the pump/valve via a BDR91 (single zone for now) given that it has it's own blending valve it would meter down the hot water when the HW is on, and request what it needs as per a normal zone. This does beg the same question though, would the Evohome treat this effective BDR zone valve like it does the HR92's when requesting heat or delay the opening of the UFH valve when the normal CH circuit is drawing a high demand .

  7. #107
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    Quote Originally Posted by 1animal1 View Post
    Evening chaps

    Gus, I can't see that this is anything to do with the Atag, the boiler is a slave to the Evo OT module which in turn is a slave to the Evo Controller - the system is a CH system primarily as per the Honeywell OT instructions, when HW is requested, power shuts the CH valve and opens the HW valve in tandem (which sounds exactly as yours was). The fact that the system is now working without issue, because it's programmed for the HW to not coincide with a high CH demand, suggests Evohome gives priority I would have thought, possibly delaying the HW triggering. Unless I'm misunderstanding what you are suggesting?

    Upon thinking further, the additional UFH system under a further normally closed valve would work independent of both the HW and CH, as this would run off the main 22mm branch from the boiler and not after the CH/HW valves - initially powering the pump/valve via a BDR91 (single zone for now) given that it has it's own blending valve it would meter down the hot water when the HW is on, and request what it needs as per a normal zone. This does beg the same question though, would the Evohome treat this effective BDR zone valve like it does the HR92's when requesting heat or delay the opening of the UFH valve when the normal CH circuit is drawing a high demand .
    I think you're misunderstanding on how OT works with EvoHome and how Hot Water Priority works with EvoHome. Evohome has no support for Hot Water Priority as a feature. This is why it has to be done using zone valves and wiring. When you have a hot water demand EvoHome requests 100% flow temperature, no matter what. If there's a demand for CH, it'll still request 100% demand. It won't prioritise Central heating over hot water.

    If your valves are working as they should there should be no reason why the hot water doesn't recover quickly in the morning, as there will be no other demand on the system (As the CH Valve should have shut down).

    In terms of the UFH this should have again a NO valve on so that closes on HW demand, giving priority to the HW circuit. Then on the manifold there will be actuators for each zone, controlled by either a BDR91 or HCC80 depending on which route you go down. The EvoHome controller will then send a demand to the OT receiver at your boiler.

  8. #108
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    Thanks MTM

    I get that EHome treats the hot water as a zone (BDR91) and requests max heat, as you wouldn't want anything less for HW. My concern is born out of what was happening prior to me changing the settings. You'd think 1hr 30mins would be enough to heat the water despite CH being on high for the morning warm up - this in isolation suggests i have a valve issue. Adjusting the time and extending an extra hour prior to the high heat demand, and my HW now working exactly as it should, suggests my valves are all good and it's possibly the EHome controller wizardry?

    For my UFH, I'll be speccing a 6 port manifold which i thought would be working off a NC valve? Opening when the stat signals the BDR to open the valve. I will only be using the first 2 ports for the first two piped areas (open plan), working off the same stat initially (the Evo controller). If I decide the 2 areas need a stat each, I'll then get the HCC80 ordered together with the actuators, otherwise this can wait until zone 3 comes into play. Surely a NO valve is prevalent when i have the HCC80 with actuators?

  9. #109
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    Quote Originally Posted by 1animal1 View Post
    I get that EHome treats the hot water as a zone (BDR91) and requests max heat, as you wouldn't want anything less for HW. My concern is born out of what was happening prior to me changing the settings. You'd think 1hr 30mins would be enough to heat the water despite CH being on high for the morning warm up - this in isolation suggests i have a valve issue. Adjusting the time and extending an extra hour prior to the high heat demand, and my HW now working exactly as it should, suggests my valves are all good and it's possibly the EHome controller wizardry?
    It could suggest a number of issues -
    - Evohome isn't requesting 100% flow temperature on HW demand. The easiest way to test this would be to turn the heating off and put HW on and see if the boiler reaches TMax.
    - Your valves aren't working as they should, extending the time has then allowed the cylinder to reheat over a longer period of time. For instance if your boiler is only 18kw, some Unvented cylinder coils can be up to 24kw on a 200/250L cylinder. If your hot water and heating is going at the same time it'll take longer to reheat.

    You also have to take into consideration about the hot water. You only reheat it every other day? So usually it is probably reheating from cold. My 170L cylinder from cold takes 45 minutes to reheat on a 14kw coil, compared to a recovery of 24minutes on a 70% draw off. So if you're reheating a larger cylinder, and then drawing off at the same time (E.g. Showers in the morning) it is going to take longer to reheat.


    Quote Originally Posted by 1animal1 View Post
    For my UFH, I'll be speccing a 6 port manifold which i thought would be working off a NC valve? Opening when the stat signals the BDR to open the valve. I will only be using the first 2 ports for the first two piped areas (open plan), working off the same stat initially (the Evo controller). If I decide the 2 areas need a stat each, I'll then get the HCC80 ordered together with the actuators, otherwise this can wait until zone 3 comes into play. Surely a NO valve is prevalent when i have the HCC80 with actuators?
    No the idea of the NO valve would be to cut off the Underfloor when a Hot Water demand is on, exactly like it does on the radiator circuit. The downside to this means you'd need actuators, however they're only cheap and still can be controlled by just a BDR91 (You don't need a HCC80)

    You could actually do it using a NC valve however you'd have to get a wire from your HW BDR91 back to the UFH BDR91. And maybe i'm just complicating matters

    In simple terms, you need to switch off the flow to the UFH when there's a HW demand. Otherwise you haven't got HW priority.

  10. #110
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    Hi MTM

    I know for certain that the boiler is requesting 100%... The boiler is an ATAG IS32, so plenty big enough to feed my 250L cylinder. That aside, the way my system is set up means that when the HW is requested and the signal is sent to the HW BDR, this closes to NO CH valve and opens the NC HW valve, so it should have complete priority. Before, on the previous timings, the hot water didn't heat at all - this again makes me think that the Evohome wasn't activating the HW BDR - it was set at the same time every second day and each day is should have heated up mirrored the next. Bizarre eh?

    For ref, hot water draw off is only normal kitchen and bathroom use for now - shower to be added soon (currently on electric shower).

    UFH - Thanks for the tips! The UFH NC/NO,i suppose if i specced a NC, it would have to be changed to NO when i upgrade to the HCC80 anyway. The UFH valve will be located at the other side of the cylinder to the boiler and other valves, where my 22mm hot/cold branches terminate after being routed around the back of the cylinder. So the UFH BDR/Pump/manifold & Valve will all be in the same area (Spur to be added) - what you are saying, is wire the BDR to the pump and actuators, and the NO valve to the original terminal block in the exact config as the NO on the CH system?

    Actuators powered by the BDR - will these work like the HR92's? And which ones would i spec, i note two sizes (manifold dependent?) and NO/NC too.. presume NC.

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