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Electric Hot water tank with two heating elements

Discussion in 'Plumbing and Central Heating' started by akademos, 26 Sep 2019.

  1. akademos

    akademos

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    Hi All,

    I have a question regarding an electrically heated hot water tank.

    I'm new to DIY and this forum so apologies in advance if I have posted in the wrong place.

    There are two heating elements attached to the hot water tank. One at the bottom and one near the middle. The one hear the middle has a timer whereas the one at the bottom doesn't.

    I feel as if I have no control over when the bottom one comes on and there seems to be no way to control it.

    Is it okay to permanently turn the bottom one off and just use the middle one or are there any good reasons why I should use both?

    Thank you in advance.
     
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  3. The arrangement you have is usually installed to take advantage of lower prices 'off-peak' electricity.

    The lower element heats a full tank overnight using off-peak, the second element is usually used as a boost to heat the top half of the tank if you have used up the full tank of hot water.

    The timer on the second element is unusual unless it's a simple 1hr / 2hr type timer to prevent you leaving it on all the time.
     
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  4. terryplumb

    terryplumb

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    The bottom heater is often connected to an off peak electricity supply ,and will heat a greater volume of water than the one higher up. You must have a switch to turn it on/ off.
     
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  5. ericmark

    ericmark

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    Years ago before people had worked out how to insulate a tank it was common to have two elements one for basins which gave a small amount of hot water and one for when having a bath, it was common to have bottom one on local switch. Then as off peak came in still used two elements but bottom one was off peak and top one to heat small amount of water should you run out of off peak water. The top one was often called "Boost".

    Some times the thermostats were set to automatic use top if hot water run out with top being set to lower temperature to bottom.

    The main problem is in hard water areas the immersion heaters can fail and with auto system the user could be unaware it had failed so the automatic change over was not done in hard water areas, so around the country different methods are used, Ulster used the Wilis system where the immersion heated the tank from top down, but it never seemed to spread to mainland UK only the Irish seemed to understand how it worked.
     
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  6. akademos

    akademos

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    There is a switch to turn it on/off but it is a switch (like turning on/off a light switch). It feels that I don't know when it comes on and when it switches off. If I wanted to limit how much electricity it uses to keep my electricity bill low I can't. It must have a way of knowing when to come on and off but there is no timer on the bottom one. Does that mean that the only way to stop it coming on at night is to either turn it completely on or completely off?
     
  7. akademos

    akademos

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    Yes, the top one has a boost switch but it is a timer as well so I can set it be on between a start time and an end time.

    The bottom one is just and on / off switch with no timer in it.
     
  8. terryplumb

    terryplumb

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    .Assuming your bottom element is actually connected to an off peak tarriff ,such as economy 7, it is only energised for a few hours . Something like midnight till 6 am roughly. If your need for domestic hot water is high ,family using baths etc. ,then you would be wise to leave it switched on permanently. Once the tanks water is heated to temperature ,the elements stat shuts off the electricity .
    If you don't use bath, and have say an electric shower that heats water itself,and your requirement for hot water is low ,mainly for washing dishes say. Then its pointless to heat a full tank. Better to switch off lower element,and just use the top one ,timed for a few hours per day ,or whatever it needs to suit your demand,
     
    Last edited: 27 Sep 2019
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  9. ericmark

    ericmark

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    If the tank is well insulated then there is no need for timer, 40 gallons takes a long time to cool, so heat it up on Sunday, use no hot water and there is still hot water on Wednesday, the only reason to use a timer is either to use off peak, or because no local thermostat, and there is always a local thermostat with an immersion heater. I use oil to heat my water, so no local thermostat in the tank, so I use a timer 1/2 hour every other day to keep water warm for hand washing and extra boost on Monday to kill any bugs.

    So unless premises only used on weekend or only used in week, or bare copper with no insulation on tank, then no point in timer.
     
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  11. ianmcd

    ianmcd

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    The bottom one is switched by your electricity supplier remotely
     
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  12. akademos

    akademos

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    That makes sense. It does seem to only come on sometime between 12 and 6am so that makes sense.

    I think I'm going to experiment with switching off the botom one and seeing whether it is soutable for my hot water needs.

    Thank you.
     
  13. akademos

    akademos

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    That's a really good suggestion - thank you.

    Yes, the tank is insulated so I will experiment with not using the middle element (whichis on a timer) and just using the middle one every other day and see how long the hot water lasts.

    I wonder if it would it make any difference if I didn't use the botom one in terms of only warm water at bottom of tank and when it comes out to the taps it will be warm for a while before the hot water in the middle is reached.
     
  14. EFLImpudence

    EFLImpudence

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    The hot water comes out the top.

    You can't have hot water only at the bottom.
     
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  15. JohnD

    JohnD

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    What colour is the insulation on your cylinder?

    Because there is a thermostat, the heater only draws electricity while it is heating water. Once the water has reached the preset temperasture, it stops. Depending on the size of the cylinder, it will usually take around 90 minutes to heat.

    There are small losses depending on how good the insulation is, hence my question.

    If you have an "economy 7" or similar type of electricity tariff, it will be cheapest to use only the bottom element, during the overnight timed cheap rate, and only to use the upper one if you run out of hot water and can't wait till morning for a shower.

    Some photos would be helpful.
     
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  16. Hugh Jaleak

    Hugh Jaleak

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    As others have said, chances are you're on an 'Economy 7' or other type of Off Peak electricity tariff. The meter is switched remotely between the hours of 01.00 and 08.00hrs to cheap rate electricity, during the period traditionally there has been lower demand for power. The bottom immersion should be connected up so it is energised during this period to heat the entire tank, (and any storage heaters that may be fitted in the property).

    Idea is the heat is put into the tank/heaters overnight and available for use the next day. The top immersion is a 'Boost' facility, if you were to run low on hot water during the day you can heat the top half of the tank using full price electricity.
     
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  17. akademos

    akademos

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    The insulation is green. Will see if I can attach some photos....

    Can the pre-set temperature of the thermostat be changed?

    Yes, it's economy 7 heating. 20190927_052723.jpg 20190927_052709.jpg 20190928_061050.jpg

    20190927_052723.jpg 20190927_052709.jpg 20190928_061050.jpg
     
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