HI,
I have a solar setup, the ev charger is before the rest of the circuit so it doesn't see the solar side - this helps with the car not draining my battery first (viewtopic.php?t=2231).
I have a new question... i use a solar iboost to heat my HW, if i choose to set a program during off peak hours and my battery is discharging or charging will it still use the grid to heat up the water, my off peak hours are roughly 00.00 to 5.30
i discharge at 01.30 - 03.25
charge at 03.30-05.25
The hot water powered from battery is on a schedule of 02.15 to 4.15 but i have noticed the water isn't getting hot as its cold in the morning, is this because the battery is either charging or discharging?
Am not sure if the iboost takes the power from the battery or the grid, i just wanted to utilize the off peak rate
FYI _ i put the above in AI and it gave me this can anyone explain this in layman terms,,
CopilotHi – this is a really common point of confusion with iBoost + battery + off‑peak tariffs, so you’re asking exactly the right question.
I’ll break it down step by step and then apply it directly to your schedule, because the behaviour you’re seeing actually makes sense.
Short answer (headline)
Yes – your water not being hot is very likely because the iBoost is not drawing power when the battery is charging/discharging the way you expect.
Most iBoost setups:
Do NOT intentionally pull from the battery
Only reliably pull from the grid when there is no competing battery control
Are easily “starved” when the battery is charging, discharging, or holding the house load steady
So even though the timer is on, very little energy may actually be reaching the immersion heater.
How an iBoost actually decides where power comes from
iBoost devices work by monitoring grid import/export with a CT clamp.
Their normal logic is:
If the house is exporting → divert excess to immersion
If the house is importing → do nothing (unless in timed boost mode)
Even in timed boost mode, the iBoost:
Still measures current flows
Still limits power if it “sees” something else balancing the load
It does not have a direct understanding of:
Battery SOC
Battery charge/discharge schedules
Off‑peak tariffs
It only reacts to net power flow.
Key rule (important)
The iBoost cannot tell the difference between grid power and battery power
It only sees whether the house is importing or exporting.
Now apply this to your setup & times
Your key windows:
Discharge: 01:30 – 03:25
Charge: 03:30 – 05:25
iBoost HW schedule: 02:15 – 04:15
Let’s walk through what the system “sees”.
02:15 – 03:25 (battery discharging)
During this period:
Battery is actively supplying the house load
Household consumption is being balanced by discharge
Net grid import/export is often near zero
From the iBoost’s perspective:
It does not see “spare power”
It does not see clean grid import for boost
So it heavily throttles or stays off
Result: Immersion barely heats
03:30 – 04:15 (battery charging)
Now the opposite problem:
Battery is pulling energy into itself
The inverter is prioritising battery charging
Any headroom is taken by the battery first
From the iBoost’s perspective:
It sees controlled flow with no surplus
Battery charging takes priority over diversion
iBoost output is reduced or cut
Again: very little energy to the immersion
Why the water stays cold
An immersion heater typically needs:
2–3 kW continuously
60–90 minutes to meaningfully heat a tank
What your iBoost is probably delivering:
Short bursts
Few hundred watts
Frequently interrupted
So although the timer is on, the delivered energy is tiny.
Does the iBoost take power from the battery?
In practice:
No – not intentionally
It does not request energy from the battery
It gets overridden when the battery is active
Any battery‑sourced power reaching it is accidental and very limited.
Why off‑peak doesn’t behave how you expect
Off‑peak tariffs work best when:
Loads are direct grid consumers
No other system is “optimising” power flow
But your:
Inverter
Battery schedules
Export‑limiting logic
…are optimising against the iBoost.
How to make this work properly (practical options)
Best option (most reliable)
Use a standard immersion boost from the grid during off‑peak
Disable iBoost during off‑peak window
Let the immersion pull directly from the grid
This guarantees:
Full power
Known energy cost
Hot water every morning
Many people do:
iBoost for daytime solar
Traditional timer/relay for cheap‑rate grid
Good alternative
Pause battery charge & discharge during HW window
For example:
Battery idle: 02:00 – 04:30
iBoost boost enabled
Grid supplies immersion cleanly
This only works if your inverter allows:
True idle mode
No background compensation
(Some don’t.)
Less reliable
Leave everything as‑is and extend the window
(e.g. 02:00 – 05:30)
This sometimes works, but it’s unpredictable.
Bottom line
Your observation is correct
The behaviour is expected
The iBoost is being starved by battery activity
Off‑peak + battery + diverter requires explicit prioritisation
If you want, tell me:
Battery/inverter model (e.g. Fox ESS H1/AC1)
iBoost model (original / + / Buddy)
Whether you can set battery to idle
…and I can suggest exact timings that will actually give you hot water every morning.
CopilotHi – this is a really common point of confusion with iBoost + battery + off‑peak tariffs, so you’re asking exactly the right question.
I’ll break it down step by step and then apply it directly to your schedule, because the behaviour you’re seeing actually makes sense.
Short answer (headline)
Yes – your water not being hot is very likely because the iBoost is not drawing power when the battery is charging/discharging the way you expect.
Most iBoost setups:
Do NOT intentionally pull from the battery
Only reliably pull from the grid when there is no competing battery control
Are easily “starved” when the battery is charging, discharging, or holding the house load steady
So even though the timer is on, very little energy may actually be reaching the immersion heater.
How an iBoost actually decides where power comes from
iBoost devices work by monitoring grid import/export with a CT clamp.
Their normal logic is:
If the house is exporting → divert excess to immersion
If the house is importing → do nothing (unless in timed boost mode)Even in timed boost mode, the iBoost:
Still measures current flows
Still limits power if it “sees” something else balancing the load
It does not have a direct understanding of:
Battery SOC
Battery charge/discharge schedules
Off‑peak tariffs
It only reacts to net power flow.
Key rule (important)
The iBoost cannot tell the difference between grid power and battery power
It only sees whether the house is importing or exporting.
Now apply this to your setup & times
Your key windows:
Discharge: 01:30 – 03:25
Charge: 03:30 – 05:25
iBoost HW schedule: 02:15 – 04:15
Let’s walk through what the system “sees”.
02:15 – 03:25 (battery discharging)
During this period:
Battery is actively supplying the house load
Household consumption is being balanced by discharge
Net grid import/export is often near zero
From the iBoost’s perspective:
It does not see “spare power” It does not see clean grid import for boost So it heavily throttles or stays off
Result: Immersion barely heats03:30 – 04:15 (battery charging)
Now the opposite problem:
Battery is pulling energy into itself
The inverter is prioritising battery charging
Any headroom is taken by the battery first
From the iBoost’s perspective:
It sees controlled flow with no surplus Battery charging takes priority over diversion iBoost output is reduced or cut Again: very little energy to the immersionWhy the water stays cold
An immersion heater typically needs:
2–3 kW continuously
60–90 minutes to meaningfully heat a tank
What your iBoost is probably delivering:
Short bursts
Few hundred watts
Frequently interrupted
So although the timer is on, the delivered energy is tiny.
Does the iBoost take power from the battery?
In practice:
No – not intentionally It does not request energy from the battery It gets overridden when the battery is activeAny battery‑sourced power reaching it is accidental and very limited.
Why off‑peak doesn’t behave how you expect
Off‑peak tariffs work best when:
Loads are direct grid consumers
No other system is “optimising” power flow
But your:
Inverter
Battery schedules
Export‑limiting logic
…are optimising against the iBoost.
How to make this work properly (practical options)
Best option (most reliable)Use a standard immersion boost from the grid during off‑peak
Disable iBoost during off‑peak window
Let the immersion pull directly from the grid
This guarantees:
Full power
Known energy cost
Hot water every morning
Many people do:
iBoost for daytime solar
Traditional timer/relay for cheap‑rate grid
Good alternativePause battery charge & discharge during HW window
For example:
Battery idle: 02:00 – 04:30
iBoost boost enabled
Grid supplies immersion cleanly
This only works if your inverter allows:
True idle mode
No background compensation
(Some don’t.)
Less reliableLeave everything as‑is and extend the window
(e.g. 02:00 – 05:30)
This sometimes works, but it’s unpredictable.
Bottom line
Your observation is correct
The behaviour is expected
The iBoost is being starved by battery activity
Off‑peak + battery + diverter requires explicit prioritisation
If you want, tell me:
Battery/inverter model (e.g. Fox ESS H1/AC1)
iBoost model (original / + / Buddy)
Whether you can set battery to idle
…and I can suggest exact timings that will actually give you hot water every morning.