@trbob I realise that this thread is a bit old but I have a similar problem with the Legionnaires cycle taking too long. In particular, it is the initial immersion bit which takes 1 hour to get from 50c to 54.5c.

Did you every resolve your issue with the legionnaire Cycle?

Hi Richard, what I do now (I'm on Octopus Cosy) is to have my Hot Water come on at 12:45pm (heated by the ASHP, the load isn't too bad in the first 15 minutes) and my Legionella Cycle is set to come on at 1pm and lasts for 2 hours. It will let the ASHP get to 51.5 before switching to the immersion element. This seems to be the best way I could find of doing it. I noticed a few weeks ago that it got up to temperature on the Legionella cycle relatively quickly as it was a fairly mild(ish) day, it's a shame that it doesn't end the cycle itself as we could have banked some heating before 4pm. 

@trbob Thanks. Does that mean your system reached the 60c within the 2 hours?

Not sure if I understand your last comment concerning ending the cycle.

According to my Ecodan Legionnaire settings, it's supposed to reach 60c and the stay there for 5 minutes. After 5 minutes it should end the cycle. Unfortunatley, in my case it never reaches the 60c before tiiming out at 2 hours.

@richard24738 Yes it's usually 59 or 60 thereabouts (or sits at 59.5 for ages, not drawing any power), yes mine is set for 5 minutes as well I think, but it has never to my knowledge ended the cycle, it just times out in the end at 3pm.

@trbob Sounds like the software is switching off the immersion at 59.5c and as it's not reaching the desired 60c, it continues with the cycle waiting to reach 60c, which never comes, and times out after the 2 hours.

I wonder if we are the only Ecodans with this problem?

@richard24738 My next L cycle is tomorrow conveniently, I'll try to keep an eye on it to see what it does.

I lowered the temp to 60 (the lowest it will go) for today's cycle. It got to 58 in the expected amount of time, then the element went off and came on after a while, did a bit more and went off again and again it hit the end of the 2 hour window.

I called Mitsubishi and the tech logged in to have a look at it. He seems to think that it may be either the immersion element or some faulty wiring causing the problem. He recommended getting an accredited installer out to look at it rather than Mitsubishi (wait times and £292 fee).

He also said that they normally set it to come on in the early morning, which I might as well do now that the Sun (significant PV power) is gone until Spring. Probably the 10pm to midnight Cosy slot as we don't have the heating on then.

Speaking of which, I asked why we can't have the heating on when the ASHP switches to the immersion element in the L cycle and he said that it's just how their systems are set up unfortunately.

I'll tag @transparent too as there is some cross over with the other thread we've been using.

@trbob I went down the Mitsi Engineer route unfortunately with the fee.

Report has just come in to say that the immersion had "irregular figures when carrying out Ohm check" so essentially saying faulty immersion heater.

Posted by: @richard24738

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"irregular figures when carrying out Ohm check" so essentially saying faulty immersion heater.

Eh?

It's just a coil of wire.
How the heck do you get 'irregular figures"?

Check what I said here about Richard's heater being rated by the manufacturer at 3000watts at 240v and 2700watts at 230v

I realise it's actually being driven by an AC waveform, but a quick rule of thumb indicates:

3000 watts of power divided by 240v gives us 12½ Amps  [Power in watts = volts x amps]

240v divided by 12½ Amps gives us a (DC) resistance of 19.2 Ω   [R=V/I]

So if I disconnected the immersion heater from the mains, and put a meter across the Live & Neutral terminals I'd expect to see a reading around 20-ohms-ish.
Bear in mind that this test is being done on a heater whilst it's cold, and that the resistance is likely to be lower when hot.

The two other possible readings are:

Zero ohms if it's a short-circuit, in which case the fuse/trip should've blown

100,000 Ω or more which is typical of an open circuit when the wire coil is broken

Does 'irregular' mean that none of those three options was encountered?
If so, then why can't a £300 engineer's inspection provide you with the figure? 🤔