Mitsubishi Ecodan immersion heater

[NightMail]

Hello all,

I am based in Ireland and signed up to the BuildHub forum yesterday.

 

We have a Mitsubishi Ecodan air source heat pump and I have noticed that the immersion heater was used quite often during a recent cold period, when overnight temperatures ranged from about -4 degrees C to -8 degrees C.

 

The multitude of manuals that came with the heat pump refer to the immersion as a booster heater but I have not been able to find any explanation, apart possibly from Legionella prevention, of the conditions that cause the immersion heater to be switched on.

 

Any comments or suggestions appreciated.

[Kelvin]

Here’s a thread on the subject. 

[akjos]

There is usually a setting in the ASHP unit where you can specify under which temperature conditions the booster heater should be used for DHW. This is usually meant for very low outside temperatures, where you don’t want the ASHP stopping your central heating in order to heat DHW. So the unit can use the booster heater in those situations and not have any down-time in your central heating.

 

My Midea unit has these setting in the controller, though I’m not sure how the Mitsubishi is configured, or if it is configurable at all.

[joth]

First thing is to confirm what your DHW Tank temperature target it set to. If this is >50 it maybe the ASHP struggles to achieve it so switches to immersion.

 

It's helpful to confirm if you have an immersion heater (in the UVC), a booser heater (in line in the primary pipework), or both? See diagrams below.

If it's a Booster heater, is maybe coming on because it's struggling to reach heating target temperature.

 

 

 

Also check these  Auxilliary settings - the DHW Delay can be used to delay the Booster/immersion coming on, to give the ASHP a longer run time to reach target.  You need to ensure the DHW max runtime is high enough for it to run that long

 

Also there's a setting 

[PhilT]

17 hours ago, Kelvin said:

Here’s a thread on the subject. 

Sounds like the solution is as per the conclusion of this Oct 28, 2021 thread - you need the latest software version 15. Assuming you have the Legionnairs cycle switched on, your Ecodan heat pump should take the DHW up to around 55 (flow temp max. = 60) when the immersion will kick in for the last few degrees, signified by the appearance of a lightning bolt symbol appearing in the FTC6 controller panel. But you should no longer see any other form of operation of the immersion heater unless you manually select hot water temp above around 55. I've switched off the LP cycle on my Ecodan - waste of time and money in my opinion.

Edited January 22 by PhilT

[NightMail]

Many thanks to you all for your responses.

 

The company that installed the heat pump is to pay us a visit, as the system is still within warranty, so I should have a better idea of the situation in a few days time.

 

With regard to your various queries:

• Kelvin & PhilT: When the installer calls I will ask if the heat pump software should be updated to the latest version.
• joth: The DHW temperature is set to 50 degrees C. It seems to me that the heat pump does not have an inline booster heater, only an immersion heater. There is an external switch labelled "immersion" which may be the simple way that it is controlled. I will ask the installer if it can be switched off.

Best regards & thanks again for the responses.

 

[NightMail]

Unfortunately, at this stage no clear resolution yet.

 

The installers have suggested two possibilities: firstly, that a service may be needed, as the initial installation was in February 2023, and, secondly, that the quantity of gas in the system may be a bit low. The service company is to to pay a visit.

 

Also, the ratio between delivered and consumed energy has dropped to ~2.91 for January 2024, which is down from ~3.49 for December 2023 and ~3.42 for 2023 overall. It seems to me that the increased immersion use probably contributed to the drop for January 2024 but the need for a service or low gas in the system might be factors too.

 

Best regards

[akjos]

@NightMail are you still seeing high usage of the immersion heater even with warmer outdoor temperatures?

 

It's absolutely normal for your COP to fall in the colder months.

Edited January 26 by akjos

[HughF]

‘Low on gas’ - what a load of horse shit…. Where do they find these people.

 

As for it needing a service - that’s purely cleaning the filter ball or y-strainer. There’s nothing else to do that can affect performance. And people wonder why the industry has a bad name, did these people used to sell double glazing in the mid 90’s….. probably.

 

You cannot check the charge on a monobloc like you would a regular hvac system (not a mini split) by monitoring the superheat, because they all have a refrigerant receiver built into the side of the compressor, the same as a mini split. The only way to verify the charge is to evacuate and refill off the scales, and no-one will do that this side of the pond.

 

January was cold, of course you’ll see a worse COP….

Edited January 27 by HughF

[NightMail]

Thanks for your responses and my apologies for not replying before now.

 

Since the weather became somewhat milder I have noticed that the immersion heater was in use only once, on Tuesday last, for space heating, while the DHW was at the required temperature, water heating was in standby and the outside temperature was approximately 5 degrees C, see attached photo.

 

The ex "mid 90's double glazing" salesperson is to call tomorrow so hopefully a resolution will be found!

 

Best regards.

[PhilT]

There was another thread on this recently. I have an FTC6 controller and my understanding is that the lightning bolt symbol denotes that the hot water immersion heater is on. Is there some kind of heating circuit immersion heater - where is it - can you see it installed in the heating circuit somewhere?

 

[NightMail]

As predicted the immersion coming on had nothing to do with a lack of gas, a point also made by the service man when he arrived.

 

As far as I understand the situation there were two settings that contributed to the immersion being turned on. Firstly, the ambient temperature setting was set to 5 degrees C and secondly, the length of time that was allowed for a temperature increase in the flow and return pipes was set at 30 minutes. The former setting was reduced to 3 degrees C and the latter increased to 60 minutes.

 

Another period of sub-zero temperatures is forecast to start on Sunday February 11, which should test the above explanations.

[NightMail]

Even though the cold weather that was forecast failed to arrive in any strength, it is looking likely that the recent adjustments to the heat pump settings have resolved the problem with excessive use of the immersion heater.