Rectifying Quiet and Low Tariff mode fault with a Grant Aerona3 controller

I have a Grant Aerona3 6kW heat pump it works well but the Quiet and Low Tariff mode do not work on these units, Grant says they have only become aware of this fault since I have pointed it out to them.
They have been trying to engage with the OEM Chofu in Japan but they have not managed to rectify the problem. I like the unit but would like these functions to work. I am now talking about compensation which I would like to use to solve this.
I presume I need a software engineer?

A “software engineer”? Who doesn’t have the source code to an embedded system, or proprietary manuals, or understanding of how it works?
This isn’t going to be an hours work. You probably need an electronics guy too.
And a lot of money, while they dig into the systems with the HP.

Realistically, this is non-starter, if you are into software/electronics and have weeks to kill “scratching your own itch” (as the open source saying goes), that’s one thing. But employing people to do it for you is going to very expensive, very quickly.

It will be cheaper to rip out the HP sell it and get a new one fitted which definitely does what you want. That way you know exactly how much it’s going to cost up front.


My thoughts exactly. The UK dealer is best placed to solve this problem, I’d expect them to have access to information and contacts that you @Gavthegas will probably never have as the end user. If they can’t get or find a solution, you’re going to have to take @Vster’s advice or live with what you’ve got.


Thanks for the advice I will give up on trying to get these functions to work.

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So, these units have a function that limits the maximum compressor speed and max fan speed to reduce noise at night etc?? I am unfamiliar with details of grant. Almost all ASHPs have this facility. Surely Grant designed this correctly? Have you ruled out a simple solution? I could believe that some UK installers don’t know how to set it up…surely it’s simple?

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The unit has definitely been wired correctly, Grant has also tried at its training centre and not managed to get these functions to work. The good news is Chofu have just been back in contact with Grant and they appear to now be taking things more seriously.
Having the monitoring has made it very easy to demonstrate these functions do not work so a big thank you to everyone.

It was a simple solution in the end. The Grant controller has an internal timer for both Eco and Quiet mode if these are set

for permanently on then the external switching works. None of this is in the Grant manual and I am the first person in six years that has pointed this out.

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Hi Gavin,

I found the same issue yesterday, where can you find the timers in the Grant controller?

Hi Nodewynd,
I found this Chofu manual helpful.
The Grant control and instructions are dreadful, it comes across as a half finished beta product that got rushed to market. I use the external smart switching so just have the times set to permanently on, I have not done it but you could probably link out terminals 28 and 29 for the night mode or 30 and 31 for the low tariff mode and use the timer in the Grant controller saving yourself some money and a few watts. Page 40 in the Chofu manual will be of interest.

Chofu-Operating-Installation-Manual.pdf (3.15 MB)

Many Thanks Gavin,

I already have low tariff PCB contacts wired to a sonoff smart switch ready for use with HA and the existing Intelligent Octopus integration that turns the heat pump on/switches batteries to charge etc.

The installers were clueless, asked Grant who gave a vague answer about a tariff that never existed and never pulled the control cable I asked them to.

Now I have found this site I will need to do some reading.



Yes that what i tried, working it with Tariffs, peak time demand and how dirty the grid was.

The problem i found is if the unit was running above 50%, say running at 70%, it would drop it t 50%.
If the unit was already running at 40%, it would do nothing.