Ecodan immersion replacement - help

[Tadpole]

Hello. I've been a member here for some time but this is my first post.

 

Based on considerable reading here (mostly) and elsewhere (a little) we had an 8.5kW Ecodan with 300l cylinder installed in our well-insulated new build in north Wiltshire. We also installed a 9.5kW Givenergy battery, Givenergy hybrid inverter, 20 Solarwatt 360 panels in a SW facing roof, a myenergi EDDI and ZAPPI.

 

It took me and our installer 5 months to persuade Mitsubishi to commission the heat pump and cylinder. Once the sun came out earlier this year I decided to make sure that EDDI was working correctly which I suspected was not the case. With help from myenergi I managed to prove to myself that although EDDI was trying hard, the immersion was not doing as instructed. On close inspection, I discovered that the over temperature cutoff had tripped and was not resettable. I sourced and installed a replacement but still no immersion. 

 

I am really keen to use EDDI to run the immersion for our hot water as since the beginning of April the heat pump has been used primarily for hot water and hardly any heating. We've exported 325kWh since 1st April so there's plenty of surplus.

 

Meanwhile I had placed a support request on Mitsubishi for a warranty replacement of the immersion. Separately, i have twice tried to order a service contract. Two online forms and a couple of phone calls later I was told my warranty request had been "escalated" - this was about 5 weeks ago.

 

So, now bored with it all I've decided to arrange for a local tradesperson to replace the immersion heater. In my ignorance, I don't know if this is a wet plumbing job or a dry electrician job. Any and all help and advice or recommended installer details will be very gratefully received 

 

Thanks

Derek

 

[ProDave]

It depends what is wrong, the wiring?  The setup?  the immersion thermostat or the actual immersion element.

 

Only the latter is strictly a plumbing job requiring the tank to be drained and a large immersion heater spanner, but many electricians will do that better than plumbers will fault find the wiring.

 

If you want to tackle it yourself give us more information and photos and do you have any test equipment like a multimeter?

 

If the over heat trip on the thermostat won't reset then it is faulty, but how do you know is has not reset without any testing?

 

If you just want it done, just call a trusted electrician.

[JohnMo]

1 hour ago, Tadpole said:

EDDI

I have found over the last year or so, when you have a battery a diverter isn't the best. Reason, your battery is fully charged before you start to export, then the diverter will start dripping electric to heat to immersion. I have found using the battery power works way better. Firstly you get full immersion power every time it switches on. I don't get paid for export so I want to make best use it and let the least amount get by.

 

So I use a measure of state of charge and PV power, so for immersion to start battery has to be at 98% and if PV is generating 1kW the immersion is switched on and stays on until the battery depletes to 94%. I also use similar to get ASHP to run at a higher demand temperature.

[ReedRichards]

When trying to heat my water with excess solar electricity I tripped the over-temperature cut-off on my immersion heater on many occasions.  But I was always able to remove the cover, press the little rod-like button and it reset.  Why was yours no resettable in the same way?  

[JohnMo]

3 hours ago, Tadpole said:

On close inspection, I discovered that the over temperature cutoff had tripped and was not resettable. I sourced and installed a replacement but still no immersion

Have you done the basic test try to run off the mains directly?

 

The cutoff is part of the thermostat, so if that has been replaced either the immersion is broken (test as above) or it's not wire correctly.

[Tadpole]

Thanks for all the prompt replies. I just need a few days to recover from a hospital op today and I will start with @JohnMo's suggestion. Once resolved I'll see if I can emulate @JohnMo's suggestion about an algorith, which should be possible as i use Home Assistant.

 

@ProDave The overheat had tripped and what would have been the push to reset plastic 'thing' was bent and distorted.. The overheat probe and trip were a clip in replacement. I do know that the immersion used to work as we used it a lot before being commissioned. You used those magic words "trusted electrician" which regrettably I'm not confident in.

 

Again thanks.....  I was a little disappointed to not receive any responses about the service from `Mitsubishi. While I think their solution is not bad, if I had known how apalling their after-sales service was, I would have bought something else.  I suspect it is perhaps insider knowledge.

[JohnMo]

5 minutes ago, Tadpole said:

Home Assistant

I use this in home assistant to start immersion and stop immersion - may not be the best automation, but works

 

alias: Immersion On
description: Immersion on at 97% and 1000W
triggers:
  - trigger: state
    entity_id:
      - sensor.givtcp_soc
    to: null
  - trigger: state
    entity_id:
      - sensor.givtc_pv_power
    to: null
conditions:
  - condition: numeric_state
    entity_id: sensor.givtcp_soc
    above: 97
    below: 101
  - condition: numeric_state
    entity_id: sensor.givtcp_pv_power
    above: 1000
  - condition: sun
    before: sunset
    before_offset: "-02:00:00"
actions:
  - type: turn_on
    device_id: immersion relay
    entity_id: 90c9027a99ba569016742b380d47d115
    domain: switch
  - action: notify.mobile_app_xxx
    metadata: {}
    data:
      message: immersion on
mode: restart

 

Then use another automation to switch off

 

alias: Immersion Off
description: Immersion on at 95%
triggers:
  - trigger: state
    entity_id:
      - sensor.givtcp_soc
    to: null
conditions:
  - condition: numeric_state
    entity_id: sensor.givtcp_soc
    below: 96
  - condition: sun
    before: sunset
    before_offset: "02:00:00"
actions:
  - type: turn_off
    device_id: immersion relay
    entity_id: 90c9027a99ba569016742b380d47d115
    domain: switch
mode: single
 

[trialuser]

I have just replaced the immersion cut out on my 8.5 ecodan 250L cylinder. It is just a safety cut out, set to about 80C I think. (see pic) There is no way to set the desired temp on the cutout. The water temp is set in the ecodan controller and it gets the signal from a thermocouple in the cylinder, which switches a contactor feding the immersion. You cant connect the feed from the diverter directly to the immersion, it has to go through the contactor which means you need to change the settings to tell the unit to use immersion for hot water, not the ashp and set it to be on during solar hours. This then stops the ashp ufh circuit from working as it thinks it needs to heat the hot water. 

I replaced it with one which has the conventional temp settings and also a safety oveheat cutout enabling a direct connection to immersion from the diverter.

https://www.ebay.co.uk/itm/223408932236 It's a simple dry plug and play push in replacement.

[ProDave]

9 hours ago, trialuser said:

I have just replaced the immersion cut out on my 8.5 ecodan 250L cylinder. It is just a safety cut out, set to about 80C I think. (see pic) There is no way to set the desired temp on the cutout. The water temp is set in the ecodan controller and it gets the signal from a thermocouple in the cylinder, which switches a contactor feding the immersion. You cant connect the feed from the diverter directly to the immersion, it has to go through the contactor which means you need to change the settings to tell the unit to use immersion for hot water, not the ashp and set it to be on during solar hours. This then stops the ashp ufh circuit from working as it thinks it needs to heat the hot water. 

I replaced it with one which has the conventional temp settings and also a safety oveheat cutout enabling a direct connection to immersion from the diverter.

https://www.ebay.co.uk/itm/223408932236 It's a simple dry plug and play push in replacement.

That's interesting.  I have never seen one that does not have a temperature dial.  But the standard Cotherm thermostat used in almost every other UVC with a conventional thermostat and the over heat trip should fit as a direct replacement.

 

Is there a separate thermostat?  I think Megaflow for instance have the thermostat remote from the heating element.

[JohnMo]

Another good reason not to put all your eggs in one basket with integrated packages from one manufacturer. 3rd party cylinder this kind of issue doesn't exist. You can also remove any control of immersion from the heat pump - so many people also have issues with immersion taking over due to settings not being optimal for heat system or DHW. 

[trialuser]

Yes there is a seperate thermostat - but Mitsubishi call it a thermocouple so I suppose it is not just a bimetallic type thermostat. It measures the temp of the water and passes it on to the controller which then decides whether or not to switch the contactor depending on what temps / settings are programed. Not sure where it is.

On mine, the only feed to the immersion is via the diverter so it can only switch on when electricity is being diverted or if I switch the diverter to manual overide.

Edited 11 hours ago by trialuser
added bit

[ProDave]

6 minutes ago, trialuser said:

Yes there is a seperate thermostat - but Mitsubishi call it a thermocouple so I suppose it is not just a bimetallic type thermostat. It measures the temp of the water and passes it on to the controller which then decides whether or not to switch the contactor depending on what temps / settings are programed. Not sure where it is.

On mine, the only feed to the immersion is via the diverter so it can only switch on when electricity is being diverted or if I switch the diverter to manual overide.

So it sounds like when using immersion to top up heating because the HP can't cope or the settings are sub optimal, it relies on the temperature probe to control the temperature.

 

I would not be happy with using that immersion with an EDDI without first fitting a normal thermostat with a temperature dial to it.  It is quite possible that the reason the over heat tripped was because you put too much heat into it with the EDDI and the water reached the trip level because there was no other thermostat to stop it.  On more than one occasion (like a recent holiday) the tank had maxed out at the set thermostat temperature as no HW was being used and a lot got exported in a few days.  With no conventional thermostat on the heater you had a potentially dangerous situation.

 

I would expect somewhere, hopefully very prominent, in the user instructions, with that configuration warning you not to use that immersion heater for anything else.

[trialuser]

1 hour ago, ProDave said:

 

I would not be happy with using that immersion with an EDDI without first fitting a normal thermostat with a temperature dial to it.

 

 

I agree with you, that is exactly what I have done, although you may be replying to the OP