Hot water cylinder using a lot of power

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#2260970 19-Jun-2019 16:49

Rikkitic:

Yeah, I was completely freaked when I discovered it. Clearly it had been like this for years. Our farmhouse would literally go up like a torch. The interior walls are old rimu planks, not gib. We cut some out when remodelling and it burned like it was impregnated with accelerant. Very old and dry.

Had similar issue with flat I was renting in my younger days, in a house that had been (illegally I decided in hindsight) divided into two flats. Fixed wired-in "Zip" hot water cylinder in the kitchen where thermostat malfunctioned and boiled dry burning out the cylinder from the inside. Never did find where in the overall house the fuse for this was supposed to be. Got home from work on a Friday evening and found acrid black smoke through whole flat from the ceiling down to about half a metre off the floor, with the cylinder glowing red. Only minutes away from catching fire I believe.

I was actually supposed to be out of town that weekend, but due to a last minute change of plans decided to go Saturday morning, rather than straight from work on Friday evening. If I hadn't returned Friday evening, I don't think I would have had any possessions left come the end of the weekend.

(Sorry to hijack thread)

Jase2985

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#2260975 19-Jun-2019 17:08

@Aredwood thanks for the response

Its not leaking water anywhere, i watched the meter for about 10 minutes and it didnt move a mm.

Its not using excessive power all the time, only when its actually heating the water, which is in line with our normal usage which hasnt changed.

You can see here that the peaks are much heigher now than they use to be, i just want to know what or where the issue could lie

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#2260979 19-Jun-2019 17:18

Jase2985:

@Aredwood thanks for the response

Its not leaking water anywhere, i watched the meter for about 10 minutes and it didnt move a mm.

Its not using excessive power all the time, only when its actually heating the water, which is in line with our normal usage which hasnt changed.

You can see here that the peaks are much heigher now than they use to be, i just want to know what or where the issue could lie

Looks like an element problem to me as a 3kw should not draw 7.5kw.

usually when elements fail it's a no go at all, not a go twice as fast.

Other things to keep in mind, thermostats fail, tempering valves also fail constantly delivering cold water to the HW cylinder.

You could try changing the element yourself, but keep in mind a specialist tool is usually required to remove the element, and they can be problematic to remove depending on how the element has failed.

Post a picture of the old element if you can when it gets replaced.

richms

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#2260982 19-Jun-2019 17:24

This is why the previous exemption of hot water from RCDs was a very bad thing.

That excess current will be going thru the earth, and if there is anything bad with those connections livening up your plumbing etc.

Richard rich.ms

Aredwood

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#2261023 19-Jun-2019 17:38

What is the sampling interval of the X axis? As maybe the thermostat now has more hysterisis than previously. And the longer run times (but less often) means that the on periods now cover multiple time blocks.

What are you using to measure and produce the above graph? As it is also showing you that your baseload power consumption has also approximately doubled. So surely your power bills will also be much higher now.

A sparky can easily do a current draw test and an insulation resistance test on the element. Which will tell you if the element is OK or on the point of complete failure. But no point in getting a sparky out, if you are using some sort of 3rd party power measurement device. Which has become inaccurate.

Amosnz

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#2261035 19-Jun-2019 18:20

The graph is an online plot from the device manufacture (efergy.com), I have one also and from memory it samples something like every 6 seconds by default.

There is a voltage setting in My Settings but I dont know if it affects the graph, I've altered mine to test but I need to wait for the spa heating cycle to start as that's the only circuit I currently monitor.

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Jase2985

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#2261036 19-Jun-2019 18:24

Aredwood: What is the sampling interval of the X axis? As maybe the thermostat now has more hysterisis than previously. And the longer run times (but less often) means that the on periods now cover multiple time blocks.

What are you using to measure and produce the above graph? As it is also showing you that your baseload power consumption has also approximately doubled. So surely your power bills will also be much higher now.

A sparky can easily do a current draw test and an insulation resistance test on the element. Which will tell you if the element is OK or on the point of complete failure. But no point in getting a sparky out, if you are using some sort of 3rd party power measurement device. Which has become inaccurate.

sampling rate is every 6 seconds using the previously mentioned power monitor. i put the extra hysterisis down to winter vs summer, maybe only an hour difference, in the middle of the night when no water is being used, between top up heats. the current on time is slightly less than it was in summer.

As mentioned above, and efergy home kit. ive compared it to what my UPS reads when i turn on and off the PC and its about inline with the power draw there.

As for the base load, DVS running in heat recover mode in winter vs in summer when its off, we also have a new fridge, plus a few more other gadgets around the house with small standby power draws which all add up.

ill test the power monitor again on a few different known resistive loads, but im pretty sure its ok.

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richms

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#2261046 19-Jun-2019 18:46

Looking at the instantaneous draw on the power company meter should tell you straight away if the other measurements are accurate or not.

Richard rich.ms

JeremyNzl

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#2261051 19-Jun-2019 19:05

I've had an element burst, We have very hard water.

The worst one I had i heard a buzzing and removed the circular cover and when re energising the cylinder there was a very small continuous arc,

On removal, external element cover had split exposing a chalk type substance and the resistive coil,

I did not test the draw I just swapped it out, Lucky to have a 50mm socket in the workshop.

If a 3kw element is drawing 6kw, I would turn it off till I got it replaced. after my experience.

I have my hw now on an rcd,

Amosnz

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#2261058 19-Jun-2019 19:29

Jase2985:

ill test the power monitor again on a few different known resistive loads, but im pretty sure its ok.

Also check the voltage setting under My Settings. I changed mine to 110v to test and the kw halved on the graph, I changed it back to 230v and the graph went back to normal.

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Jase2985

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#2261081 19-Jun-2019 20:12

yea i checked that and its set at 240v

JuanPerez

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#2261174 20-Jun-2019 00:25

Looking at the two graphs, it's not just the peak that are higher (close to double), the baseload also shows the same pattern. In Jan the baseload looks about 0.6kW, whereas in July it appears to be over 1kW (a bit hard to tell exactly).

Are you sure it's not something wrong with the way the power is being measured (or being displayed)?

mclean

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#2261392 20-Jun-2019 11:51

If you really want to test it yourself: Isolate all the circuits at the switchboard except the HWC, turn on all the hot taps to cool down the HWC, and see how fast the meter goes. (I'm assuming you're not on a controlled hot water tariff - if you are then this might not work straight away). Otherwise get a sparky to tong-test the HWC circuit.

A stable 3.5kW fault would be a very rare thing indeed!

tripper1000

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#2261493 20-Jun-2019 14:16

As an electrical guy let me echo what others have said, elements don't fault and double in power consumption long term. They might briefly as they burn out, but not for days or weeks on end. In this failure mode they usually pop the fuse/CB in seconds as current draw goes from 13 amps to 26 amps. Likewise the internal conductor in the element can not withstand 26 amps and often burns out before the CB has a chance to break the circuit, which means but the time an electrician checks the element, it is almost always open circuit. (The switch-melt failures are usually caused by degrading contacts in the switch being unable to carry their rated current).

A 3kw element can not draw 6 kw long term as it will simply burn out. This looks very much like an instrumentation error.

Building on what mclean said above, compare what your house electricity meter says and compare it to your metering gadget. I bet you 1x chocolate fish that the power companies meter will read 1/2 of you internet connected metering gadget.

Another way to check your meters calibration and the H/W current draw is to by/borrow a clamp meter like this one.

Irrespective, the hypothesis that the element drawing 6kw is causing a rise in power the bill is fundamentally flawed. Even if the element was drawing 6kw long term through some fluky series of coincidental faults (or someone sneakily changed it when you weren't home) , the result is 6kw of heat which will simply heat the water faster, and reach the thermostat shut off temp in 1/2 the time and the net change in power consumption would be negligible.

pctek

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#2261512 20-Jun-2019 15:01

Jase2985:

timmmay:

What did your plumber say?

good question, but plumbers dont deal in electricity

Oh yes they do. All plumbers replace elements. You don't need to be a full electrician, just limited.

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