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We have a new 11.2 kW Ecodan ASHP and all UFH in concrete floors in a large well insulated house. I started with Weather Compensation and was satisfied, with little cycling, but decided to try Advanced Auto Adaptation extending the cable from the little FTC box, moving it into the living room. It is working great, using low power and no cycling. The only con is that as there is no connection from the existing house thermostats to the FTC, I have to keep the living room thermostat set the same as the FTC thermostat so they switch off at the same time when the room temperature target is reached, otherwise the UFH pump will run unnecessarily, although it doesn't use a lot of power. I now intend to order a Mitsubishi wireless controller and receiver (£167). Any comments?

We have identified the problem. By bypassing the house wiring with a long cable, everything works ok, showing there is a short somewhere in the house wiring. This is not easy to find, and probably requires new wiring round the outside of the house. An easier solution is to use Advanced Auto Adaptation, which does not have a connection from house thermostats. So I have been trying it out with a long cable to the little FTC box moved to the living room. It is great! Low power and no cycling on our all-UFH system. So I will order a Mitsubishi wireless controller and receiver (£167) and go for that.

Hi Roadrunner, on the WC LHS view screen, if you keep pressing the F4 (right hand) arrow, you will eventually walk down the slope and can see the WC temperature target for every outside temperature. It's not for editing. Re the FTC mounted on the Hydrobox ( I don't have one), I would expect this to be warmer than ambient, and of no use in controlling the heating. I have been trying out the Advanced Auto Adaptation, extending the cable from the little FTC box and moving it into the living room. With our setup (all UFH in concrete floors), it's great, low power and no cycling. The only con is I need to keep the existing living room thermostat a little higher than the FTC "Room Temperature", as if I don't, my thermostat may switch the UFH manifold pump off, the flow temperature would go up quickly and the FTC will switch the HP off for a while, as the connection from my existing thermostats to the FTC is removed on AAA. I am now going to order a Mitsubishi wireless controller and receiver (£167 at heatpumps.com), and make it permanent.

If your ASHP is already running at it's lowest power, reducing the flow will cause it to cycle. In that situation I think it's better to run it at a flow rate that avoids cycling, and let the floor heat to your required temperature and shut down for a few hours.

When you have to get a new heat pump after repairs to the heat exchanger and the compressor failing, as we have had to after 12 years of use, you will realise that short cycling is bad. It also means that your UFH is periodically getting colder flow water which slows down the warming of the room. I discovered that ours was short cycling when we got a smart meter and I tried to prevent it. I'm sure it caused our problems. I did the heat loss calculation and got a lower power unit. Now it only cycles off once or twice a night, but it's early days yet.

As your MELCloud shows the same 22.5C for both zones, I'm guessing that your room thermostats are not the source of those readings, and the 22.5C is coming from the thermostat inside the little FTC box (mounted on the bigger FTC controls box, near the Hot water cylinder?). If you are on room temperature mode, then the heat pump will be controlled by those temperature readings. Try using the Weather Compensation mode if you are not already, as that will ignore the "room temperature". See YouTube videos on how to adjust. Don't lower the WC curve too much or the HP will cycle on and off frequently (bad). Too high and you will be spending more on electricity. I'm not sure about the settings you show, perhaps you should talk to mitsubishi if you still have a problem.

You may have a problem others have had here. Your Heat Pump may be trying to complete the Legionella cycle and heat to 60C, with the help of the immersion, as the HP can't reach 60C itself. Sometimes the immersion overload clicks out so it doesn't heat, and the heat pump never reaches 60C, but keeps trying to. Our immersions have a reset button inside the cover (turn it off at the wall switch first!!). Or the immersion might be faulty and need replacing. I hope this helps.

The installer came and spent a lot of time on the phone to mitsubishi but did not fix the problem. Then I had an idea, I bypassed the wiring with a lead direct from the FTC to the nearest Heatmiser, and everything worked ok, proving that there is a wiring issue. Should have thought of it sooner but I hadn't found a fault with my tester - it must be a high resistance short. Now waiting for the electrician to come.

I have FTC6 but I'm sure it's the same. The "Room Temperature" is using a thermistor inside the little FTC box. So it shows the temperature of wherever that is mounted - usually on the FTC Electrics box, which is often mounted on the Domestic Hot Water Cylinder. The little box can be located 10 metres away with a long cable which might be enough to put it into a living room, but unless you are going to use Auto Adaptation (is it available on FTC5?), there's no point. Just ignore it and use Weather Compensation which is very good, but takes a lot of patience to optimise. Be careful not to set it too low or your HP will be cycling on and off frequently which reduces the life of the (expensive) compressor and heat exchangers. Cycling also reduces efficiency and raises energy consumption. I see you have a buffer tank which should reduce cycling. However, if you set the WC too high, your HP will go to a higher power level, also costing money. To adjust the WC, look at the YouTube video https://youtu.be/-983aLzVZ_I?si=guJZxm1B8xbrnAL- Mitsubishi Weather Compensation Adjustment, by Mark Sawyer. With mine, I have a MELCloud app which shows me when it's cycling, and a Smart meter which shows the approx power level. Mitsubishi sell a power energy monitor but I think you need the MELCloud app to use it. As others have said, you don't want your radiator trvs to be turning on and off too much, which could also cause cycling, better to balance down the rads (turn down the flow valves) in all the rooms where you only need background heating, so they heat a little, all the time the heating is on, and set the trvs a little higher. In the main living room, if there are trvs, set them to max, and rely on the room thermostat which I assume is connected to the FTC to stop operations when heat is not required. If you have good house insulation (!!) it's cheaper to run the ASHP most of the time at the lowest flow temperatures you can, without much cycling. I hope your heat pump has been sized correctly because they are often too high powered which will cause them to cycle. However they do have variable speed compressors to adjust the power required. There are lots of helpful videos on YouTube. Good luck.

Thanks JohnMo, the new Ecodan which replaced a 13 year old Ecodan, is plumbed to UFH and DHW each via 2-way valves. There is no buffer tank. The Heatmiser signal wires are connected to IN1 in the FTC. They only call for heat. Thanks Bozza, the timers are now only in the FTC, and are working ok, except that when the timer turns on the UFH, it heats immediately and continuously whether or not heat is being called, until the timer turns it off (or an upper limit is reached). The important phrase in your comment is "...and is calling for it". It seems our room thermostats/ Heatmisers are being overidden by something. The installer is coming tomorrow, so I hope he has the answer!

Our new Ecodan ASHP is heating when no heat is called. Set for Weather Comp, with Heatmiser UH8 wired to IN1, after power connection the FTC6 screen turns on only when heat is called (which indicates that the Heatmiser signal is ok). However, it heats from the start of the timer schedule whether or not heat is called (and even if the Heatmiser is disconnected), and only stops heating at the end of the timer schedule. It seems that some setting is overriding the Heatmiser signal. The wiring and settings all look ok, and the actual heating is working as expected, as is the DHW. I am waiting for the installer and expect a full reset is required but would appreciate any suggestions.