I too use MELcloud exclusively to schedule temp changes and over night set back.  Yes,  very occasionally it misses a beat and the times that I have been able to pin it down were mini and intermittent internet connection drops. I put that down to the quality of the wet string that Openreach use to get what they laughingly call an internet service to the back of beyond. It is equally possible the failure may on occasion be the signal from Mitsubishi.  It has never been too much of an issue to follow up. 

@downfield my understanding is that you can have a maximum of 4 heating time slots on the FTC and that it does not rely on the internet to send the instructions to the Ecodan.
So, if your requirement is only 2 time slots, then using the FTC would avoid any risk of losing an instruction to internet failure.

@richard24738 Richard, last winter I was on weather compensation and without any set back other than on Tapo SRV's in some unused bedrooms. Over the summer I changed the buffer tank to volumiser, introduced a Mitsu wireless controller and changed to Adaptive control. I then introduced HavenWise and this is on 24 hrs.

So probably too many changes at one time and I am considering going back to basics. In this respect, could you please remind me if you can not only set a time, but a setback temperature on FTC? I only recall setting operating times and not temperatures in the set times 

@davidalgarve Hi David. On my Ecodan I use Adaptive which allows up to 4 heating time slots to be specified on the FTC. For each time slot you enter the required room temperature. Set back is as simple as setting a time with your set back temperature

So in my case I currently have 3 settings 00:00 18c, 04:00 21c, 13:00 22c. Just to explain, the 22c at 13:00 is active until the next instruction at 00:00.

The timings are influenced by the Octopus Cosy "Cheap periods" and that we are home all day and like to be warm.

I have used 5 timings on Mel-Cloud in the past when playing around with the cheap cosy sessions but found it didn't make much difference and we did have an internet issue which meant that the pump didn't receive its instructions. FTC avoids internet issues.

@richard24738 Thank you very much for the info. I only had a short time on Adaptive before starting a trial with HavenWise so had not tried this.

I didn't recall, in previous years, having the ability to select temperature when I was using Weather Compensation (without the wireless controller).

As much as I would like to, I can't play around with it at the moment because I am having some difficulties with HavenWise control

@davidalgarve I don't think you have as much control with weather compensation. Definately not setting a room temperature as temp is from the curve but not sure about timing.

I did try Havenwise for a while and found it useful and the guys really helpful.

However, I wasn't ready to give up control at that point and had a bit of difficulty understanding the logic behind when it wanted to heat the hot water. It started in the afternoon (logically as its warmer) but my requirement was for early morning showers which meant that the water had about 17 hours to cool down with hand washing, etc.

The solution was to up the required water temperature which didn't sit right. It may have been more economical but didn't feel right and gave the risk that someone could draw the water during the afternoon or evening and we were left with cold morning showers. Of course things may now have changed with their algorithms.

Posted by: @richard24738

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@davidalgarve I don't think you have as much control with weather compensation. Definately not setting a room temperature as temp is from the curve but not sure about timing.

I did try Havenwise for a while and found it useful and the guys really helpful.

However, I wasn't ready to give up control at that point and had a bit of difficulty understanding the logic behind when it wanted to heat the hot water. It started in the afternoon (logically as its warmer) but my requirement was for early morning showers which meant that the water had about 17 hours to cool down with hand washing, etc.

The solution was to up the required water temperature which didn't sit right. It may have been more economical but didn't feel right and gave the risk that someone could draw the water during the afternoon or evening and we were left with cold morning showers. Of course things may now have changed with their algorithms.

Without disagreeing with anything you've said there, @richard24738, there is one thing I'd point out.

When I look back historically, our DHW accounts normally for between 1.5 and 4 kWh leccy (absolute max was 11.2 kWh) and an average of 3kWh. Given any energy efficiency savings will be based on minimising heat loss through the cylinder's insulation and given most cylinders are pretty efficient these days at retaining heat, even if my setup isn't optimally efficient, the potential saving is never going to be bank-breaking.

Our setup triggers a DHW heating cycle (up to 50 degC) whenever the hot water temperature drops by more than 8 degC. We have some prohibited times for DHW heating so that we can guarantee the water's reheated after the last shower of the evening (and so is hot enough for someone to have a shower in the morning), that no reheating happens during the expensive part of the morning or afternoon and that the DHW reheating doesn't interfere with the heat pump's recovery from a mild setback overnight to daytime room temperatures. Whilst it may not be absolutely the most efficient financially it definitely is the most effective for the household and the cost from any loss of efficiency is only a handful of pence.

@richard24738 We also want hot water for 7:00am showers and we have a cheaper tariff from midnight until 7:00am.

Havenwise choose to heat the water just after midnight rather than my previous choice of 5:00am.

Our tank is in an outside "pumproom", so how do you decide between my choice of minimising the time when losing heat from the cylinder and their choice of accepting the heat loss and operating the heat pump more efficiently at, possibly, higher ambient temperatures that might occur at midnight as opposed to those at 5:00 am? 

Posted by: @richard24738

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Definately not setting a room temperature as temp is from the curve but not sure about timing.

Just catching up with this thread as I am still having problems.

A question on the above comment, though:  I thought that the WC curve defined the flow temp, which is independent of the room setting?

I use MELcloud to set a room temp of 21C for 18 hours and currently the WC curve shows a flow temp of 35C or so, return about 32C.

This works 95% of the time, but occasionally there is no step up in the a.m. or no set back at 2200.

This issue continues - 3 days ago no heating on at 0500 and so on waking I had to increase the room temp on the MELcloud app to get the HP spinning.

So I contacted MEL support  and got the following response:

You need to run the system in Auto Adaption mode for the target temps. set on schedule to be achieved.

Please call our homeowner helpline on 0161 866 6064 to help with this.

I find this difficult to understand, so went back with

I tried auto adaption a while ago and it reduced the COP.  Can you explain a bit more why the WC setting won’t follow the time schedule?  It doesn’t seem to make sense and works 90% of the time.  Why does it suddenly fail?

This got the same unhelpful response:

Auto adaption mode is the only heating mode programmed to hit target temperature set on the schedule.

Please call our homeowner helpline on 0161 866 6064 to help with making sure your system is set-up correctly.

Is this correct?  If so, what's the point of the WC option?

And why does it work fine most of the time?

@downfield I wonder if it is the MELCloud app that is the problem? It is not the greatest bit of software. I was using weather compensation all last year with the operating times set on the FTC 6 rather than the MELCloud app and it never failed. The responses you received were disappointing and suggested that they did not read your question. 
Out of interest what CoP were you getting on Auto adopt? With Havenwise operating on Auto adopt, I am now getting average of 3.4 but appreciate your AAT’s are lower than mine