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Thread: Help with Evohome / Opentherm / Intergas

  1. #71
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    Quote Originally Posted by paulockenden View Post
    Don't forget that the proportional band is only 1.5 degrees. Any zone further out than that and the boiler will be going full-pelt.
    I have to wonder if a common(ish) cause of this is having a zone with an undersized radiator or an over optimistic set point. If the radiator is not physically capable of reaching the set point or can only barely reach it with the radiator going full pelt it would result in a permanent ongoing "maximum heat" demand from the boiler.

    Our hallway is a bit like that - in the middle of winter it struggles to reach a real (measured with a remote sensor) 20 degrees, so I schedule it to 19 degrees instead. Otherwise the boiler is going flat out to achieve the un-achievable, and never drops below maximum demand.

  2. #72
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    That sounds almost identical to my tank(albeit 10y old) - which is working very well with the HW control. I'm in a S plan.

  3. #73
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    Think we will be. 2 x motirised valves, not the unreliable 3 way one.

  4. #74
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    You can't have a 3 port valve on a unvented cylinder anyway, so you'd have to either have, 2* 2 Port Motorised valves or a 3 port and a 2 port after that one. The latter is a nightmare to wire and a stupid way of doing things.

  5. #75
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    Quote Originally Posted by mtmcgavock View Post
    You can't have a 3 port valve on a unvented cylinder anyway, so you'd have to either have, 2* 2 Port Motorised valves or a 3 port and a 2 port after that one. The latter is a nightmare to wire and a stupid way of doing things.
    This is not entirely true.

    G3 regulations don't actually state you need a 2 port valve. What the regs say is that the heat demand to the coil needs to be removed when there is a high limit situation. This can actually be achieved by rotating a 3 port valve 180 degrees so the closed port is on the hot water side instead of heating. It is loosely called 'D-Plan' after Dan from Jennings Heating who came up with the idea (although others claim they were doing it earlier).

    I actually prefer hot water priority with a 'inverted' 3 port diverter valve - works much better with OpenTherm and evohome.

    As for OpenTherm, evohome and Intergas... I have all 3 things working just perfect in our training facility! 👍🏻

  6. #76
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    Any reason why they are all working 'perfectly'?

  7. #77
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    Quote Originally Posted by The EVOHOME Shop View Post
    This is not entirely true.

    G3 regulations don't actually state you need a 2 port valve. What the regs say is that the heat demand to the coil needs to be removed when there is a high limit situation. This can actually be achieved by rotating a 3 port valve 180 degrees so the closed port is on the hot water side instead of heating. It is loosely called 'D-Plan' after Dan from Jennings Heating who came up with the idea (although others claim they were doing it earlier).

    I actually prefer hot water priority with a 'inverted' 3 port diverter valve - works much better with OpenTherm and evohome.

    As for OpenTherm, evohome and Intergas... I have all 3 things working just perfect in our training facility! ����
    Sorry I have to disagree with that, I think you'll find that every Unvented cylinder comes supplied with a 2 Port valve, along with clearly stating in the instructions that the valve must be fitted. As you state that regulations say that the heat demand needs to be removed, by fitting a 3 port or even diverter valve cannot guarantee this. Many 3 port valves pass on the HW side not providing a full shut off, along with the fact that in case of power loss to the 3 port valve it will fall to it's naturally open position which is HW. This then isn't closing the circuit, where as that a 2 port valve would close. Should power continue to a heat source (Such as the Boiler relay) it could prove quite deadly.

    The fact that you are advising people to do this is quite frankly worrying. If you want HW Priority just wire the system accordingly with the 2 Port valves.

  8. #78
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    Quote Originally Posted by mtmcgavock View Post
    Sorry I have to disagree with that, I think you'll find that every Unvented cylinder comes supplied with a 2 Port valve, along with clearly stating in the instructions that the valve must be fitted. As you state that regulations say that the heat demand needs to be removed, by fitting a 3 port or even diverter valve cannot guarantee this. Many 3 port valves pass on the HW side not providing a full shut off, along with the fact that in case of power loss to the 3 port valve it will fall to it's naturally open position which is HW. This then isn't closing the circuit, where as that a 2 port valve would close. Should power continue to a heat source (Such as the Boiler relay) it could prove quite deadly.

    The fact that you are advising people to do this is quite frankly worrying. If you want HW Priority just wire the system accordingly with the 2 Port valves.
    I'm sorry but this is showing a lack in your knowledge not mine.

    I have stated that the 3 port valve would have to be reversed 180 degrees so the 'open' port 'B' is on the heating side and therefore when the power is cut to the valve it closes the hot water port - absolutely no different to a 2 port. I have seen many cases where 2 port valves have failed open and the fact most 3 port valves are made with the very same mechanism as most 2 port valves (I have only ever fit Honeywell valves) makes what I have described no different. It is just an intelligent way of looking at the problem and finding an engineering solution.

    People like to make their own regulations up in the heating industry and there is nothing wrong with what I have suggested. As for unvented cylinders, unless you have completely bypassed the T&P valve by capping it off and also removed the high limit thermostat on the boiler, I can't really see how a 'deadly' situation would occur? More likely an immersion heater to cause issues with unvented cylinders than a gas boiler ever would.

  9. #79
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    Quote Originally Posted by The EVOHOME Shop View Post
    I'm sorry but this is showing a lack in your knowledge not mine.

    I have stated that the 3 port valve would have to be reversed 180 degrees so the 'open' port 'B' is on the heating side and therefore when the power is cut to the valve it closes the hot water port - absolutely no different to a 2 port. I have seen many cases where 2 port valves have failed open and the fact most 3 port valves are made with the very same mechanism as most 2 port valves (I have only ever fit Honeywell valves) makes what I have described no different. It is just an intelligent way of looking at the problem and finding an engineering solution.

    People like to make their own regulations up in the heating industry and there is nothing wrong with what I have suggested. As for unvented cylinders, unless you have completely bypassed the T&P valve by capping it off and also removed the high limit thermostat on the boiler, I can't really see how a 'deadly' situation would occur? More likely an immersion heater to cause issues with unvented cylinders than a gas boiler ever would.
    So when you've fitted the reserved 3 port, what happens when someone else, who isn't the original installer comes along when the valve has failed and says this hasn't been fitted correctly (Not aware of the situation). He then puts it on the right way round and leaves it - your are opening a can of worms.

    I've seen many situations where a 3 port valve has been fitted to a unvented cylinder where the high limit stat has cut out and heat still being transferred. On one particular occasion where a Worcester had been fitted with a pump over run and no bypass so it was pumping the heat round the cylinder. On this one it was discharging at a considerable rate, should that T&P failed it could have lead to a serious problem.

    Another occasion where a Viessmann boiler with internal diverter had been fitted, the temperature sensor had fallen out and the HW left on constant. Resulted in the cylinder overheating with no thermal cut off. Had a 2 port valve been fitted following the manufacturers instructions it would have prevented this.

    Whilst I agree it is very unlikely a deadly situation could occur as a number of components in the chain would have to fail, starting to deviate from the manufactures instructions shouldn't occur. The regulations are there, but the manufactures instructions should be followed. If you had an issue down the line they'd be very quick to say it wasn't fitted correctly. As gas safe always state with gas appliances, always follow the manufactures instructions.

    Use a 3 port valve, but put a 2 port valve before the cylinder. At least then should anything change on the installation that's out of your control you've always got the fail safe of the 2 port valve.

  10. #80
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    How exactly would an unvented cylinder overheat to the point of dangerous pressure release when heated by a closed loop to a boiler ? It can't get any hotter than the flow temperature of the boiler - which unless the boiler is faulty, is going to be under 90 degrees. (So now you have two separate devices failing at once to cause a problem, and that's pretty hard to protect against)

    From an electric element its possible, yes, because the electric element can reach several hundred degrees...

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