Ecodan r32 keeps flipping into immersion mode.

[MorganP]

Morning hive mind - really hope you can help.

 

We have a Ecodan r32 installed about 3 years ago. Not long after, it would occasionally flip into immersion mode and need restarting. Since then it has gradually got worse and is now happening every day or two. Some details

 

- no faults showing

- legionella mode set to 30 days

- Heating is auto adaptive mode

- House has rads upstairs, UFH down

- Stats run through wireless UH8-RF V2

- Seems worse when stats are calling for heat. When all stats are off then it doesn't happen so often

- immersion mode doesn't seem to heat the water either - only around 18 degrees

 

We've spent hundreds on not getting it fixed so need a different route! Original installers not very helpful; charge for call out but don't fix issues. We have a decent freelancer who does the annual service but he doesn't seem able to fix it either. 

 

My wife is now threatening to take the kids to live in a hotter country (again).

[JohnMo]

It has to be a basic setting messed up.

 

Let's go back to basics

Why is the immersion there - to provide additional heat when the heat pump isn't working or cannot provide enough energy heat the house.  It is activated based on timers based on getting temperature water flow temperature up to an expected level.

 

You can have the immersion heater modes set various ways and for various times.

 

I would get the manual out and have a good read, understand what is happening.  Post your settings on here - possibly your manual also.

 

17 minutes ago, MorganP said:

legionella mode set to 30 days

Unless you have health reasons to use it, I wouldn't bother with mode - do a risk assessment - many available online.

 

Also are you talking about your heating or domestic hot water?

[MorganP]

56 minutes ago, JohnMo said:

Also are you talking about your heating or domestic hot water?

 

Thanks John.

 

Our Heat Pump does both heating and hot water but I'm not sure what immersion mode is trying to do when it kicks in. Maybe just supply the domestic hot water. Either way, it doesn't work as it never gets above 20°

 

I'll have a proper look through the settings and report back. 

 

[JohnMo]

So if DHW and it's only getting to 20 degs good chance it is a time related issue.  Also check your diverter valve is moving from heating to hot water production.

 

So dig out all the DHW settings 

[Dillsue]

Can you alter the hot water schedule to come on during the day when you can watch what happens when it tries to heat the hot water?

 

There Should be little need for space heating just now so I would focus on getting the hot water up and running. Do you know what the "stats" do as you shouldnt need them if running in auto adaptive mode.

 

If you're really under pressure to get this sorted I would contact any local Heat Geek engineers and see if they have Ecodan experience and can help out.

[-rick-]

Just now, Dillsue said:

There Should be little need for space heating just now so I would focus on getting the hot water up and running.

 

My reading of the OP is that the heating is still working (as a heat pump) but there are spurious activations of the immersion during which time the system doesn't heat up.

[Dillsue]

4 minutes ago, -rick- said:

 

My reading of the OP is that the heating is still working (as a heat pump) but there are spurious activations of the immersion during which time the system doesn't heat up.

OP says "it doesn't heat the hot water either" so I assumed it's CH and DHW??

[-rick-]

3 minutes ago, Dillsue said:

OP says "it doesn't heat the hot water either" so I assumed it's CH and DHW??

 

'In immersion mode' which it only sometimes switches to.

 

8 hours ago, MorganP said:

it would occasionally flip into immersion mode and need restarting. Since then it has gradually got worse and is now happening every day or two.

 

- immersion mode doesn't seem to heat the water either - only around 18 degrees

 

So my reading is that the system works fine for a while then something happens and it stops working as normal and needs resetting and then it works again.

 

@MorganP can hopefully confirm.

[MorganP]

3 hours ago, -rick- said:

So my reading is that the system works fine for a while then something happens and it stops working as normal and needs resetting and then it works again.

 

This is correct, thanks Rick. The heating and hot water work well when the ASHP is running. The issue is that the ASHP randomly cuts out and flips into immersion mode. Given that immersion mode never gets above 20 degrees, it's effectively useless at that point. It kicks back in after I restart the system. The installer annoyingly put the main controller in the garage next to the tank - always fun being out in my dressing gown first thing in the morning

 

 

6 hours ago, JohnMo said:

So if DHW and it's only getting to 20 degs good chance it is a time related issue.  Also check your diverter valve is moving from heating to hot water production.

 

So my Ecodan set up should (I think) have the water on permanently. It's set to heat to 50°. It then has a 10° drop off before kicking back in, and presumably going back up to 50. That seems correct because when it's working, the water is rarely below 40° according to the MelCloud (Mitsubishi) app. I'm not sure how to manually check the diverter valve but I'm pretty sure that's fine too as the heating works well when the ASHP is running.

 

Hmm, so very frustrating. 

 

 

[Wil]

Is the immersion broken/ failed and when the heat pump goes to call it on (legionella?) it doesn’t heat up and trips out in fault?

[MorganP]

4 hours ago, Wil said:

Is the immersion broken/ failed and when the heat pump goes to call it on (legionella?) it doesn’t heat up and trips out in fault?

 

Thanks again for the feedback. There's no fault showing but your point does flag two things that aren't necessarily related.

 

Firstly: I think the immersion may be faulty as it doesn't get over 20 degrees. I can't see a specific immersion temperature setting. I assume the Ecodan controller would try and use the immersion heater to get to the regular tank temp of 50°. If so then it's not working properly. If anyone knows how it's meant to work I'm all ears!

 

Secondly: Even if true, I can't see how the above issue wouldn't be the reason it trips into immersion mode in the first place. 

 

 

On 08/09/2026 at 17:06, Dillsue said:

There Should be little need for space heating just now so I would focus on getting the hot water up and running. Do you know what the "stats" do as you shouldnt need them if running in auto adaptive mode.

 

@Dillsue - following this comment I'm trying to isolate the issue. For now I've switched off the heating all together on the controller. I did think that auto adaptive mode would use the stats though. There are three modes - fixed flow, compensation curve and auto adaptive. I assumed all three would still need the stats to call no?

[-rick-]

Change one thing at a time but another thing you could try is to disable the legionaire cycle (I don't know the heatpump but I imagine it might be possible it has tried to use the immersion for that, detected some fault and got into a loop where it keeps retrying).

[Dillsue]

1 hour ago, MorganP said:

@Dillsue - following this comment I'm trying to isolate the issue. For now I've switched off the heating all together on the controller. I did think that auto adaptive mode would use the stats though. There are three modes - fixed flow, compensation curve and auto adaptive. I assumed all three would still need the stats to call no?

The 3 modes you mention can all likely run without a stat but your installer may still have put one or more in. Have you got multiple stats suggesting you've got zoned heating? This is unlikely to be relevant whilst you are trying to get the DHW sorted.

 

In your first post you say the system started with this issue soon after installation?? Did the installer not sort it out then, or try to??

[Dillsue]

1 hour ago, MorganP said:

Firstly: I think the immersion may be faulty as it doesn't get over 20 degrees. I can't see a specific immersion temperature setting. I assume the Ecodan controller would try and use the immersion heater to get to the regular tank temp of 50°. If so then it's not working properly. If anyone knows how it's meant to work I'm all ears!

 

Secondly: Even if true, I can't see how the above issue wouldn't be the reason it trips into immersion mode in the first place. 

The immersion may or may not be faulty but theres likely another fault as the HP should be able to heat the DHW way beyond 20 degrees without needing the immersion....there's no point in having the heat pump if it's going to default to using the immersion!