Geyser Power Usage

I’d appreciate any thoughts on the following:

After recently installing an 8KW Sunsynk inverter and 5kW battery power usage of my 4KW geyser has increased significantly!

Prior to installing the inverter and battery the average daily usage of my geyser hovered around 5Kwh (May and June).

Since installing the inverter and battery the average daily usage is between 15kwh and 20kwh (last two weeks).

I have a CBI timer installed which is set to turn the geyser on between 05h00 and 07h00 and then again between 15h30 and 20h00. These settings have remained the same before and after installing the inverter and battery.

It’s worth noting that the electrician rewired my DB when installing the inverter to spilt essential from non essential loads.

Any ideas what might be causing my power usage to have increased so much? Could it have something to do with the wiring of the DB?

Any thoughts would be highly appreciated.

I will hazard that the thermostat is coincidentally acting up (something like the contacts are welded in the closed state) keeping the element permanently on as long as the timer switches on (4kW x 6.5h ~ 26kWh).

Without the timer and depending on water draw from the geyser you might find constant water dripping via the pressure relief valve.

5kWh for a geyser is very low. A standard 200l geyser will use at least half that just for standing losses. But if we assume there is no standing loss, 5kWh should be enough to heat 100l from 10°C to 55°C, so 15-20kWh could be a lot, but that depends on how much you use. Remember it also got a lot colder in the last couple of months, which means you have to heat the water more and people also usually use more, take longer showers etc. But I don’t see how this is related to the installation of an inverter.

How are you measuring how much power the geyser uses?

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I have a CBI timer installed on the geyser which reports daily consumption.
As indicated the timer has been reporting an average usage of 5Kwh per day prior to installing the inverter and strangely 15-20kwh afterwards.
The increase therefore seems to have something to do with the inverter installation.
Perhaps something like the thermostat has somehow been ‘fused’ on when rewiring of the DB took place? Alternatively it may just be coincidental?

How does the timer report consumption??

Timer reports energy usage I mean. Sorry.

Do you have an ammeter that can measure the current drawn by your geyser (and voltage)?
I would do a test to see if the energy is the same. You’ll have to measure the time the geyser is on for and compare your calcs with the CBI Astute…

What size geyser is it?
What’s the orientation? Horizontal or vertical?
Does the water coming out of the taps seem hotter than before.
What’s your hot water consumption like?
What’s the thermostat set to.

As others have said, 5kw seems a bit low. I installed a 100l vertical geyser recently and I heat it once a day during peak solar and it uses around 6kw to heat it to about 60-65 degrees.

Unless the installer/electrician in some way wired things that the CBI timer is now actually bypassed (i.e. that the geyser element is purely left to on/off control by the thermostat) there is not realy a way that the inverter installation can increase the geyser electricity consumption.

@RichardvdS how long have you had the CBI timer? i.e. how much data do you have to compare the geyser 5kWh vs sudden 20kWh usage to? Like others have said ambient temperature change and/or warm water usage changes can also explain some increase in time the geyser element will be on for.

Assuming that you did not get a new gardener that started topping up the pool from a hot water tap ( :wink:), or the extended family came over and have 3 baths a day, or you have enough data to feel confident about the average eletricity consumption of the geyser when on the timer I would try to check if the timer and/or thermostat is functioning as expected.

  1. I am not familiar with the native CBI app but you should be able to check whether the geyser stops consuming electricity if you manually, via the app, switch the timer off during a period that the element is on (i.e. within the first 10 minutes or so after 05:00 or 15:30). → if possible double check what the app reports with your electricity meter (the app reporting zero consumption does not necessarily mean it is true).

  2. If the timer does indeed stop the electricity feed to the geyser, then also check that the timer does operate according ot the set times (I think the timer is internet dependent, so a network problem could mean that the timer functionality is not operating correctly).

  3. If the timer does what it is supposed to I would check the thermostat functioning. - easiest will be the 15:30 time slot. When the timer switches on at 15:30 the element will very likely be switched on by the thermostat. For the next hour or so do not use the hot water taps, and check whether the geyser stops consuming electricity after some time. If it does not stop at any stage it would suggest a problematic thermostat. If the thermostat does switch off the element it, does not yet rule out a thermostat problem as it can be an intermittent issue, so check a couple of times.

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5kWh is very low. 4kW element usually means a 200 liter tank, so the standing loss should be around 2.2kWh a day, leaving you with 2.8kWh for water heating. 1.16Wh per liter per °C. Assuming ambient at 15°C and heating to 55 (delta = 40), 2800/40 = 70 liters of hot water.

Doable for an energy conscientious 2-person household. Showers run 8 liters a minute, assuming 75% hot water, that’s 6 liters a minute, for a total of around 12 minutes of showering.

Now let’s assume people extend their showering time to double, and ambient is 10°C. 140 liters of water with a delta of 45, 140 x 45 x 1.16 ~= 6500kWh, plus the standing loss of 2.2, I would expect around 8.7kWh a day.

So… assuming the initial and the later measurements were correct… I cannot quite get to 20 or even 15.

I don’t suppose the meter/switch can drill into per-hour measurements? Would be interesting to see if it behaves normally (it is on for an hour or so right after bath time), or if it constantly turns on during the day (indicating you have a water leak… or people constantly running the tap to wash their hands with warm water).

Edit: Another possibility. The rewire moved some other loads onto the timer circuit. I’d imagine you’d notice that easily though, when some stuff doesn’t work when the geyser is off.

Edit 2: There is a mistake in my math. I didn’t include the 1.16Wh factor, so my 70 liters is off. But it is off by at most 16%, and I am too lazy to mess with it now. It is not going to change the conclusion, and everything is a bad hand-wavey anyway.

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Hi All,

Thank you for the useful replies.

Out of complete desperation i ended up replacing my geyser thermostat thinking that this was perhaps faulty and not turning off once it reached its set temperature (hence the higher than expected electricity usage). This despite having tested the original thermostat to confirm it was working correctly.

After replacing the thermostat and setting it to approx 50deg i removed all timing settings and left the geyser on. The idea being that this would inform how much power (and time) it would take to raise temperature of 200l of water from approx 20 deg to 50 deg without any influence of timing settings. I then monitored the power usage via the CBI App and could clearly see the power draw of ±4kW over the next 2 hours (or so) at which point the power reduced to 0W. Considering the CBI controller was still “on”, the water had clearly reached 50 deg and the thermostat had correctly cut power to the element. The CBI App also reported a total power usage over this period of ±8kW (as would be expected).

After further interrogation of my CBI app I have FINALLY realised the following…


  1. my CBI App has two controllers linked to it i.e. 1 for the Geyser and 1 for the Pool.
  2. my DB was rewired on 09 June

When my DB was rewired in order to split loads into essential and non essential, the electrician inadvertantly switched the wiring of the two CBI controllers. Consequently the readings on the CBI Geyser App (previously pool pump) appeared to indicate an increase from 5kWh to 20kWh for the geyser. It is now clear however that the ±5kWh (prior to 09 June) is reflective of the pool pump (i.e. 0.75kW x 6hrs) and the 20kWh (after 09 June) reflects the geyser usage (4kw x ±5hrs). As these results are reporting on the same Geyser App graph it appeared that the geyser usage has increased significantly when in fact it was due to a change in wiring resulting in the geyser usage being reported alongside the pool pump values.

Similarly the CBI Pool Pump App (previously Geyser App) has reported a similar trend with readings dropping from ±20kWh (prior to 09 June) to ±5kWh (after 09 June).

Finally SOLVED!!!

Thanks for everyones replies.



That is FAR more believable. Working from my own pool pump, 1.2kW motor, runs 4 hours a day. That’s about 5kWh :slight_smile:

so, technically I was correct that the geyser was filling (the data of) the pool… :thinking: :crazy_face: :wink:

thanks for the feedback @RichardvdS and glad you got it sorted. (keep the spare thermostat somewhere safe, the new one will pack up at the most inconvenient time)

The CBI app does not give the actual consumption, it estimates from the Kw of the element and the number of hours it has been on. For e.g., if your element is 2 Kw, it will show usage of around 5 Kw if on for 2 hrs or so. Now it shows you around 20 Kwh because it was on for 10 or so hours but in actual fact, the element didn’t consume that much. Just the length of time it was on multiplied by the size of the element. To prove this, remove the wire from the CBI astute that goes to the geyser and switch it on on the app, it will still you a consumption of 5 Kw but with no hot water.


Did you tell your CBI app what the element power is? Your explanation sounds wrong.

That said, the CBI/Tuya version isnt very accurate, as in it updates very slowly, so it does come out as sort of an estimate. However, now that mine is on tasmota, its very accurate without any estimation in home assistant. Shows actual real time usage and correct kWh values.

I have a CBI timer installed which is set to turn the geyser on between 05h00 and 07h00 and then again between 15h30 and 20h00.

Tip: If you have excess Solar PV, set the timer from 11am to 16pm and use the Geyser as a “battery”

Tip 2: If you have the right system, let the solar system switch on the geyser when there is spare power.

… and if there is no spare pwoer THEN you set the geyser to heat only after optimal solar hours … or due to bad weather. :wink: