Mitsubishi Ecodan: hot water coming on outside of schedule (not due to reheat or legionnaires settings)

Morning ​@Adavison and welcome to the OVO Forum! I’ve awarded your Heat Pump badge so that other Forum members can recognise the kit you have.

I don’t own a heat pump myself, so my knowledge is limited. I’ve copied some AI generated suggestions below:

Normal behaviours

• Reheat cycle: If you have scheduled times for DHW, your Ecodan will run during that scheduled period if the water temperature drops below a certain threshold. For example, if you have it set to 50°C with a 10°C maximum drop, the system will kick in within the scheduled window if the temperature falls to 40°C.
• Priority for hot water: The Ecodan prioritizes hot water production over space heating. If there is a demand for both, the system will always heat the hot water first. The system can also interrupt space heating during a scheduled DHW cycle, depending on your setup.
• Legionella cycle: To prevent the growth of bacteria, Ecodan units are programmed to run a regular, typically weekly, cycle that heats the tank to a high temperature. This will happen outside of your regular schedule and is a necessary safety feature.
• Eco mode vs. normal mode: On some controllers, activating a "force DHW" command can override the normal "Eco" settings and cause the system to heat more aggressively. If you have "Eco" mode enabled, manually boosting the hot water can temporarily force the system into "Normal" mode.
• Automatic adaptations: If your system is running in "Auto Adapt" mode (controlled by a wireless thermostat), it may make its own decisions about when to heat the water to maintain a set minimum temperature. In this mode, the heat pump runs when it needs to, not necessarily when you program it to.
• Weather compensation and freeze protection: The system may run a freeze stat function if the outside temperature drops below a certain level. This circulates and heats the water to prevent pipes from freezing, consuming very little power. 

Potential issues

• Faulty thermostat or sensors: A malfunctioning temperature sensor in the hot water cylinder can give the Ecodan a false low-temperature reading, causing it to heat the water when it shouldn't.
• Incorrect timer settings: Double-check that you have properly saved your DHW schedule on your controller. An incorrect or unsaved schedule can lead to unexpected behaviour.
• System cycling: In some rare cases, a system fault can cause the unit to cycle on and off for no apparent reason, leading to repeated heating spells outside of the schedule. 

What you can do

1. Check your schedule settings: On your controller, navigate to the DHW menu and confirm that your scheduled heating times are correctly set and saved.
2. Adjust the reheat settings: Within your DHW settings, you can often change the "max temp drop" value. A smaller drop will cause the system to reheat more often, while a larger drop will reduce how often it turns on within a scheduled window.
3. Confirm the DHW mode: Ensure your system is set to "Schedule and reheat" mode and not "Reheat only," as some installers may leave it in this mode to avoid callouts.
4. Look for error codes: If the problem persists, check for any error codes on your Ecodan controller. Faults like a poor flow rate or failed sensor can trigger unexpected heating cycles.
5. Restart the system: Performing a hard reset of the system by turning it off at the mains for a few minutes and then restarting it may resolve temporary control issues.
6. Contact your installer: If the issue continues after checking these points, a qualified installer or service technician should inspect the system for faults in the wiring, sensors, or other components

You can also find some more information, and useful links to other similar Forum topics in this thread:

Let us know if this helps. I’m wondering whether ​@brichard  or ​@Ecodanwarrior might be able to drop in and help here as well...

Thanks ​@Ben_OVO. That’s all the things I have read and tried so far. There are lots of settings mentioned online but quite a few of them (things like setting to “schedule and reheat” mode), don’t seem to exist in real life.

I’m wondering if it’s actually possible to set the DHW schedule and still run a schedule for the space heating through the app, as setting one seems to affect the other. If anyone else has any experience with these things I’d really appreciate your help.

Cheers

Hi ​@Adavison - in the control unit if you click on the button on the far right (first screenshot) and then if on the far left (second screenshot) the DHW symbol with the thermometer shows its on this could be the reason its heating even before the temp has dropped below the 15 degree limit.

​@Ecodanwarrior what would cause that to be on? 

Could just be something an technician left on during a service.  From speaking to the person who services ours they said that they use this to stress test the system but other than that nothing else really.

Ok, I checked and it’s not on as standard and I’ve toggled it on/off again to make sure.

For a bit more context, we currently have the heating set to switch off and on again at certain times in the night as it can be a bit noisy and wake our son up as his rooms right next to the airing cupboard. It looks like the DHW is coming on when the main system switches back on again, even when the temperature is still above the reheat value. 

Does that sound like expected behaviour and is there really no way to ensure the DHW only works on schedule?

When you say heating do you mean the entire setup is powered off?

For us, I use the thermostats to control when the heating comes on and off not the control unit.  The control unit I use to set the temp in the rads.

Yeah, I set the whole system to be off at bedtime as when they have bath the DHW is normally still on when they get into bed. The best way I found to schedule it being off, is to time the whole system to shut down for an hour through the app, otherwise the DHW is still trying to get back up to temp.

I have our DHW timed on the control unit to come on for a small while in the evening and then for a few hours in the morning, it doesn’t run outside of that.  I don’t have the app so not sure if shutting down the system resets anything when it boots back up

Ok, thanks. I’ll try switching off the app schedule for now and seeing if it works just using the controller.