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Rayburn to MegaFlo System - Limited Hot Water

Discussion in 'Plumbing and Central Heating' started by DanielM88, 17 Jan 2020.

  1. DanielM88

    DanielM88

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    Hello All,

    I have a hopefully quite quick and easy question about a MegaFlo system we have got installed. The MegaFlo system is heated by the Oil Rayburn we have downstairs.

    We are finding that even after 3-4 hours of the Rayburn being on, we still only have 10-20 minutes of hot water at the most, which is barely enough for two showers.

    Could this be a problem with air inside the Megaflo system? Or some sort of setting that only allows water to be heated and filled to a certain level? The gentleman who had the house before us was single so was unlikely to use a lot of water, perhaps he has changed a setting?

    The water is plenty hot enough and we don't see much difference between the amount of hot water generated after 1 hour or 3 hours, which leads me to believe that there is something stopping it from generating more.

    Any help, greatly appreciated.
     
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  3. picasso

    picasso

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    How many litres does your megaflo hold ?
     
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  4. DanielM88

    DanielM88

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    Hi Picasso, our system holds 125 litres of water
     
  5. Pete W

    Pete W

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    What Rayburn Model is it?
     
  6. picasso

    picasso

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    If your shower is running at 10 lpm which is fairly average a 125 litre cylinder will give about a 16 minute shower, 125 hot and 40 litres cold is 165 litre , maybe time for a bigger cylinder.
     
  7. DanielM88

    DanielM88

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    Rayburn Heatranger 440K I think!

    Hmm, i did wonder whether that would be the case.

    Average shower uses 50 litres in 8 minutes apparently, but I wasn’t sure of the mix of hot to cold.

    Maybe time for an electric shower or a colder shower
     
  8. fezster

    fezster

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    Assuming megaflo is at 65 degrees and incoming cold is 5 degrees at the moment, I'd put the cold to hot ratio at 3:2, assuming a target shower temperature of 40 degrees.

    For 125L hot, you get ~ 80L cold. Most decent thermostatic showers will use about 12L/min (but can go much, much higher). So you'll get ~17 mins usage from ~200L of water. This should increase in summer as the incoming water temperature increases.

    If you have isolation valves on your shower, you could try turning them down a bit to restrict water flow - at the expense of shower performance. Or buy a bigger HW tank.

    Most modern UV cylinders are fast recovery. So if you heat them whilst using them, you may find that is adequate to continue to use the showers for longer.
     
  9. DanielM88

    DanielM88

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    Thanks everyone for the replies so far.

    I’m going to run a test to know for sure. I’m going to put the water for a couple of hours, then run a bath of purely hot water and see how I get on.

    The MegaFlo system itself has a power supply to the front, what does this do?
     
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  11. endaxi

    endaxi

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    I've had Megaflo related problems in the past and learned a lot about them with the help of forum members here. There are things you can do yourself to ensure the system works as it should. This of course doesn't mean it satisfies your needs fully. It's worth reading the manuals for both the boiler and the Megaflo. If you don't have them they should be available on the internet.

    Some things I found out are firstly that the Megaflo air gap should be regenerated once a year or so. It's quite easy and instructions should be on the side of the tank. Again, they are available on line and there's a good You Tube video which shows what to do.

    Also, I discovered that I had two thermostats on the cylinder. One for the immersion heater and one for the external heat source. In my case a gas boiler and in yours the Rayburn. I set both of mine to setting 4 out of 5 (from memory). The external thermostat is a small brass hex with a slot and is easily missed. I also discovered that the boiler stat needs to be set to a higher temp than the cylinder stat or the hot water demand will never be met. When my boiler stat was set lower than the cylinder stat the motorised valve to my heating coil stayed open and the pump ran continuously as long as my hot water was set to 'on'. I set my boiler to what I determined to be between 70 and 80c. With my cylinder stat at 4, I then get water at around 60c at the taps.

    Hope this is of some help.
     
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  12. DanielM88

    DanielM88

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    Thanks, that is a help!

    What does the immersion heater do? I assume that's what the power supply to the Megaflo powers?

    I haven't spotted a thermostat yet, but I will have a look and have a look on Youtube!

    Thanks again
     
  13. endaxi

    endaxi

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    The immersion heater is simply an electric heating element. Some cylinders may have more than one whilst others may not have one at all.

    Mine simply plugs into a 13amp socket. If I open the immersion heater cover there is a thermostat. From memory it's a plastic dial with an arrow on it. Turn the dial clockwise to increase the temperature. I only switch mine on at the wall socket if my boiler's broke or to supplement the boiler if I want to heat the water quickly.

    Inside a second cover is the external heat source thermostat. On mine it's a tiny brass nut. Again, turn it clockwise to increase the temp. Just remember that the boiler thermostat needs to be set to a higher temp or the cylinder thermostat demand can never be met.

    If you do have an immersion heater then you have two heat sources to heat the water... Immersion and Rayburn. I know nothing about Rayburns I'm afraid.

    Re-generating the air gap allows the water in the cylinder to expand when it's heated. Mine hadn't been done for years so I suffered from dripping taps and toilet overflows running into the bowl due to increased water pressure. Once I regenerated the air gap however, I introduced an anomaly of periodic hot water from cold taps... but that's another story. I found a reasonably inexpensive fix for that and I now feel confident that my Megaflow operates safely.

    Good luck with it and happy to help if I can. Just be aware I'm not a plumber... I just got interested in how my heating and hot water works.
     
  14. DanielM88

    DanielM88

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    Thanks! I have been keeping the immersion heater off when the Rayburn is on, so I'm glad that's correct! I will have a look under the cover for the thermostat later on...

    I will double check for a second cover tonight too, I couldn't see one before, but there is a temperature control on the Rayburn, so I wonder if that's the only place I'll find one.

    I made sure that the hot water was still being heated when we showered today and that seemed to do the job, okay. Previously It had gone off at the time we started showering as we wanted the heating off at that point (has to work together).

    I am going to get the Megaflo moved into the loft soon, so I'll hopefully ask them to service it at that point too, check the air gap is fine etc.

    Thanks very much for your help here.
     
  15. ianmcd

    ianmcd

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    what is the thermostat on your Rayburn set to ?
     
  16. ReJect

    ReJect

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    You really shouldn’t be working at anything to do with your Megaflo, except doing the air gap.
    The thermostats for immersion and for operating motorised valve (heat to coil from Rayburn) are part of the critical safety components of the unit.
    Only a unvented G3 qualified person is supposed to work on those. Excess heat is highly dangerous on unvented units.

    Check that no water is ever dripping into tundish, especially when cylinder is up to full heat, as this will lose you hot water and can be due to lack of air gap, or other faults.
    Note that all unvented units need serviced once a year for safety and warranty, which is usually 25 years
     
  17. SJSbuilding

    SJSbuilding

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    I have come across this problem a number of times where the family get home and the kids go to get a shower and by the time the parents want one there's not hot water left.
    The boiler needs time to heat the water up in the cylinder it not a combie boiler where you get almost unlimited hot water.
    Try taking shorter showers "Navy Showers" save water and energy
     
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