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  1. F

    Priority domestic hot water PDHW

    Replying to a slightly old post, but this is exactly what I did recently and it works fine. I used a 2NC contactor (as I have 2 CH zones) and a 3 module wylex enclosure, as the 2 module one linked to in this thread doesnt have the required depth to house the contactor. When DHW fires, it shuts...
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    Honeywell motorised valve not working correctly?

    From the FAQ sheet: https://heatingcontrols.honeywellhome.com/documents/All/pdf/975.pdf "When this Heating demand is satisfied, during a Heating ON period, 50V to 150V (voltage can vary according to the supply) will remain on the orange wire and the valve will continue to be energised and warm...
  3. F

    Low delta t

    From my experience, a honeywell ABV is very easily damaged (Im sure other brands are similar) if you try to set it incorrectly. So worth checking if it is constantly bypassing (assuming you have a bypass!).
  4. F

    Setting central heating flow temperature

    I had that exact problem with my Vaillant 438 many years ago John. Despite d.0 range rating, the boiler would first fire at X% of it's total output. A later revision of the PCB improved on this (although, it continued to be a problem to an extent).
  5. F

    Setting central heating flow temperature

    The return temperature will dictate the amount of condensing which occurs. The lower the return temp, the more it condenses (45 degrees for 90%+ condensing, 55 degrees will be less than that). However, even if the boiler is setup for 80 degrees flow temps, and assuming the system has been setup...
  6. F

    Unvented Indirect / Low Pressure

    Have they measured your incoming flow rate and dynamic pressure to ensure an unvented cylinder is suitable? It should be a minimum of around 20 litres / min with 2 bar working pressure. You will also need to ensure your internal pipework is upgraded, especially to showers which should be in...
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    3-tee rule on unvented cylinder

    The 2 port valve won't stop the reverse circulation (as the water doesnt flow through it when this occurs). The return water from the HW cylinder may go back up the return pipe for the CH (as it is the last tee). It will then flow in reverse through the radiator flow pipe to the next radiator...
  8. F

    Expansion vessel pre charge

    Would you mind elaborating on this? If your EV is charged to 1 bar and you top up the system to 1.5 bar, you are utilising the expansion capacity of the vessel when cold, reducing the amount of expansion available when hot. Is there some advantage in doing this (which is what I think you were...
  9. F

    Nest Thermostat to Control System Boiler with 2 Zone CH & 1 Zone HW

    I bought 2 of the same unit - like I said, it was more for aesthetics. The HW function is not used on the second thermostat.
  10. F

    Nest Thermostat to Control System Boiler with 2 Zone CH & 1 Zone HW

    Both thermostats will show in one app. I use 3rd gen for both u/s and d/s, for uniformity.
  11. F

    Nest Thermostat to Control System Boiler with 2 Zone CH & 1 Zone HW

    I've got the same setup. Use a second nest 3rd gen for upstairs, with it's own heatlink. The HW function is not used on this.
  12. F

    Why is my mains water PRV not maintaining 3 bar?

    Yes, if it's not drop tight, the static pressure could rise under no flow conditions. Does the pressure only rise when the unvented cylinder is being heated? If so the EV needs charging (as said above). You should also have a NRV between the cylinder and the balanced cold, to stop hot water...
  13. F

    GWS vs Reliance - Accumulator

    Does anyone have experience of either of these? Reliance – Aquasystem 500 Litre Potable Expansion Vessel XVES050150 £660 GWS Challenger 450L Accumulator Tank (same as Stuart Turner Mainsboost 450SV?) £690 Both are similarly priced. The reliance has a replaceable membrane. The GWS has a 5...
  14. F

    Replacement UV cylinder

    Thanks all. I wont go down the blending valve route having looked into what problems increasing temp causes. Thanks for pointing that out.
  15. F

    Replacement UV cylinder

    Boiler is a Vaillant 438. I'm not sure about in Summer, but I guess will find out soon enough. The kids are only just now using the shower more excessively. I will have to educate them on how HW can run out and not to spend unnecessarily long in there. I'm toying with the HW priority and...
  16. F

    Replacement UV cylinder

    Max 2 showers at once, but they are quite a high flow rate (15-20 L/min). The cylinder is set to heat up before the heating comes on. It also heats up whilst the heating is on, but I'd imagine the flow temps are substantially lower due to heating demand. I hadn't considered de-stratifying - is...
  17. F

    Replacement UV cylinder

    As the kids are growing, I'm finding our 250L Megaflo is occasionally running out of HW. What are opinions on having a second UV cylinder vs having a bigger 400/500L cylinder fitted? Any pros and cons? My Megaflo is "only" 7 years old. Is there any resale value to these things, or do I just...
  18. F

    Megaflo Eco vs Eco Plus

    You need to ensure your mains flow rate is adequate enough that the accumulator is used only to supplement it. A 500 litre accumulator only gives approx half of that in usable volume, which won't go very far with more than two high flow outlets in use. The OSO system is no doubt very slick -...
  19. F

    32mm MDPE to 2 x 22mm?

    32mm to 28mm plasson adapter. 28mm to unvented (if that's the way you go) with a 28mm balanced cold. Use a 28mm pressure reducing valve to maintain flow rates. Then appropriately sized pipes to outlets, with 22mm to showers if they require high flow rates.
  20. F

    Tun dish leaking intermittently on my Ariston Classico STI cylinder

    Some of the Grundfos Bronze pumps have intelligent software which learn your HW usage habits and then automatically start/stop at those times.

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