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Immersion heater turning on randomly

Discussion in 'Plumbing and Central Heating' started by Vanq, 8 Oct 2021.

  1. Vanq

    Vanq

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    Hi all, hoping you can help

    I've just had a smart meter installed and can now see that there is an additional draw of c.2.8-3kw randomly being used during the day for periods (can be 5 minutes, can be an hour or more), upon investigation this appears to be the immersion heater (if I use the immersion breaker on the CB then it drops back down). This appears to be drawing more power than I need for the hot water (use case is just for showers in the morning)

    I on the control (Siemens) I have this scheduled for 2.30am-4.00am to take advantage of the cheaper electricity at that time. The towel radiators (3) are also on this circuit.

    Happy to provide any details of makes/models as I can but not sure what people would need to perhaps help identify why it's doing this as it's driving the energy usage up quite considerably!
     
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  3. oldbuffer

    oldbuffer

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    1. Electricity is only cheaper in the early hours if you are on a special tariff like Economy 7 or Economy 10.
    2. Sounds as if the timer is not controlling the immersion heater, just the thermostat on the heater itself.
    3. Photographs of the timer, heater and hot water cylinder, might help.
     
  4. Vanq

    Vanq

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    1 - yes I do

    Photo's below - tried to capture the key parts but if anything more needed please do ask.

    Appreciate the help

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  5. JohnD

    JohnD

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    The timer you show is for the boiler, not the immersion heater. There is no advantage to restricting the hours of HW.

    The immersion heater should have its own switch, typically where that thick white flex goes to the wall, and you should switch it off except on those rare days when the boiler breaks down.

    The yellow pump on the hot water pipe circulates tap water round the pipes, so there is no delay when you turn on a hot tap. Heat escaping from these pipes wastefully cools the cylinder. You also seem to be rather short of pipe lagging, which wastes more heat. You could put a timer on it so it only runs when people are likely to be using the hot taps.

    You mention an MCB in the consumer unit, which I can't see.

    Are you running a hotel?
     
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  6. Harry Bloomfield

    Harry Bloomfield

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    OK, I will ask the question...........

    Why have the immersion heater enabled at all, when you have a gas boiler available to heat the water far cheaper?
     
  7. Vanq

    Vanq

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    Thanks John, really appreciate the help. Its a new house so trying to understand how it all is working. It's not a hotel, guessing you've asked with the style of the plumbing?

    I've turned it off last night using the MCB (which is just to the right of the photo with the tank it in) and still had hot water this morning, although not as hot as usual.

    Yes the system was apparently designed to have the pump move the water around to reduce delay - not something that's particularly a use case for us to be honest. There's just 2 of us, and whilst I'm at home all day with work the wife is out. A timer might not be a bad idea if its causing issues as really its only useful for washing hands but would it save any meaningful amount of power?


    On the restricting of hours of HW - could you explain that to me please? I'd have thought that having it run for a set amount of time in the morning pre showers would make most sense with possibly a top up later in the day before any evening uses (washing up etc - we're waiting for a dishwasher for 3 months already with the global issues)

    For reference, I have an Oil fired boiler with UFH

    Would it still be cheaper to use the Oil boiler as it's more efficient (?) or put a timer switch on the electric immersion heater to run, say 2 hours, between 12am and 4pm where I pay 5p per KWh due to my electricity tariff?

    Really appreciate the help!
     
    Last edited: 9 Oct 2021
  8. Vanq

    Vanq

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    That's helpful thanks, just learning about what I should and shouldn't have on as it was all set up this way when we bought it and first experience with an immersion heater as had a different system in the old house.

    I should have clarified as well, its an Oil boiler not gas (not available here). But I also get electricity for 5p per KWh between 12am and 4am as well if that factors in
     
  9. Harry Bloomfield

    Harry Bloomfield

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    Rather than a timer to set when the yellow HW circulation pump runs, it might be better to run it from PIR sensors. One in the bathroom, would run the pump when ever someone enters the bathroom. Maybe another one, over the kitchen sink, shielded so as only 'see' someone actually at the sink.

    You need to work out the cost of producing your hot water using electric, versus the oil boiler.

    Maybe your electric thermostat is set to an higher temperature, than your oil water heater?
     
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  11. JohnD

    JohnD

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    You can put a timer on your yellow pump, I think that will save a lot of wasted energy. Or just turn it off.

    As you have an oil boiler, you may as well use it.

    All the time it is running to heat your radiators, let it heat your cylinder too.

    In summer, running the boiler for an hour in the morning (before and during shower time) and an hour in the evening (before and during bathtime) will give you ample hot water for a 2-person household. If it goes cool that will be from wasting heat in your pipes. The cylinder itself is very well insulated. You may as well spend a few pounds on some pipe lagging.

    Your system is expensively built so I have no doubt that as soon as the cylinder reaches target temperature, it will turn off the boiler so you will not waste oil in summer when the central heating is turned off.

    I think you have a 250 litre cylinder, so it would take the immersion heater alone about four hours to fully heat it from cold. The boiler will be much faster.
     
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  12. Vanq

    Vanq

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    Any idea how to work the cost of electric v oil?

    Not sure there is a thermostat for the oil water heater, where might that be so I can check if you have any idea?
     
  13. Vanq

    Vanq

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    Thanks John, you've been a big help. I will look at adding more pipe lagging although the majority of the pipes without it aren't warm to the touch when I've just checked but its a great shout.

    Its a UFH system not radiators, not sure if that changes the advice? But suspect letting it just run is the best policy from your advice so far. Once I get a monitor for the oil I'll then give a try of with and without the yellow pump running to gauge that. I'm also going to try it off and see how much of a difference it makes with the hot water time.
    EDIT - will need to run the hot water on a cycle (morning/evening) else the towel radiators are on all the time (they don't have thermostat valves)


    I do have a separate question if you have any thoughts given you've seen the system - in the shower I get a burst of dripping for 1-3 minutes some mornings around 5am sometimes its later at 7am and sometimes not at all. It seems to happen less if I run cold water when finishing in the shower but still does happen periodically - my thought was it was something to do with hot water in the system (probably wrongly). Its only from the overhead waterfall shower head not the side one
    Any advice on it as its in the ensuite so wakes me up when it happens as its quite loud.
    The pressure also is markedly dropped on the overhead one verses the side one - my dad thought that might be due to smaller pipes in the install perhaps?
     
    Last edited: 9 Oct 2021
  14. Harry Bloomfield

    Harry Bloomfield

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    It should be on the side of the cylinder, measuring the cylinder's water temperature.
     
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  15. Vanq

    Vanq

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    I've got the one with a dial turned up to full, perhaps just needed more time to heat with the cycle than I gave it as previously it was getting topped up all the time with the immersion heater
     
  16. Harry Bloomfield

    Harry Bloomfield

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    Water expanding as it warms up in the pipe and expanding out of the shower head.

    Our above bath electric shower almost always does it, if I fill the bath for a bath. The extra warmth rising from the bath water, warms the water in the hose and the head starts dripping for a few seconds.
     
  17. Vanq

    Vanq

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    Anything that can be done and its really quite loud? Would it help not having that pump on which puts the hot water around?
     
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