Annoying issue with Daikin Altherma 3M Disinfection

matelodave

I like others dont run the disinfection cycle so both my back-up and immersion heater MCB's are switched off.

TBH if you've got a non-vented tank which is connected to the incoming mains, the chlorine in the water supply has  probably killed off any legionella before it even gets anywhere near your tank and as FreeBear suggest 50 degrees is plenty hot enough to kill any that have escaped the chlorine.

You may want to do a sterilisation cycle ones every couple of months if it make you feel better but once a week is really a bit excessive unless you've got a vented tank with a feed tank in the loft where you are likely to get a lot more nasties than legionella.

Exiled_Tyke

This is interesting.  So should we all set the DWH temperature to 50 degrees and not bother with the Legionnaires cycle? 

My guess with what's happening here is the immersion heater simply doesn't have enough time to get to temperature before  5,30am. 

rjmachin

I have just managed to complete the disinfection cycle.

I updated the "Comfort mode" for hot water to heat to 52 instead of 48 degrees, then started the disinfection to 60, and once it has reached 60 and maintained it for 30 minutes, the warning disappeared.

Now that the warning has cleared, I have disabled the disinfection cycle.

I have set the daily DHW to heat to economy, which is 45 degrees.

I have set a weekly DHW on Sunday to heat to comfort, which is 52 degrees.

Thank you to @matt_drummer, @Reed_Richards, @matelodave and others who have given feedback.

Does the above plan schedule sound okay?

Exiled_Tyke

The plan will be ok if the 45 degrees you've set gives you enough hot water! However if your install is like mine, Octopus set the tank to reheat if it gets too cold. (I turned this off using the installer code because if I find I don't have enough hot water I'll schedule the overnight heating to be hotter rather than having it come on during the day).  

rjmachin

I turned off the reheat as well quite quickly after the install.

I do have a mid afternoon top up as well to boost the DHW.

FreeBear

rjmachin said: I have set the daily DHW to heat to economy, which is 45 degrees.

I have set a weekly DHW on Sunday to heat to comfort, which is 52 degrees.

Does the above plan schedule sound okay?

When I had an open vented DHW, 45°C was about all I ever heated it to. Even then, it was only once or twice a week during the summer. In my opinion, the risk of legionella and other water borne diseases are minimal at best and greatly exaggerated by many.

When hot water was needed for washing up, I'd just boil the kettle (and still do). 

NedS

rjmachin said:

I am on Octopus Intelligent Go (I have an EV) so get 11:30pm to 5:30am at 7.5p per kWh.

I am not trying to heat to 60 degrees every day, it is only once per week, but is not completing and just keeps running until I force it to restart (this is my issue)

Does anybody have any ideas why it is not completing?

The tank is due to heat up (normal) between 3pm and 4pm, so if it gets hot enough, I will set it to run the disinfection afterwards.

The installer set it up to run at 4am initially, but I could do it in the afternoon if it works and take the hit on cost.

I have exactly the same issue with my system (Samsung, not Daikin) - it is never able to complete the legionella cycle and throws an error when it times out to say the legionella target temp (60C) was not reached.

The cause on my system is that my ASHP cuts out when the LWT hits 60C, meaning the hottest it will heat the DHW to is around 55C. The immersion also has a built in thermostat, and despite that being set to max, also cuts out at a tank temp of around 55C, so the legionella target temp of 60C can never be reached (56C is the highest DHW tank temp I've been able to observe).

I don't bother scheduling a legionella cycle. I just heat the tank to it's max achievable temp (~55C) whenever electricity is cheap on Agile.

I would suggest you observe what the system is doing. At what LWT does the ASHP cut out? What about the immersion (you should be able to see when the immersion is drawing power on your IHD for your smart meter, if you have one).

FreeBear

NedS said:

rjmachin said:

I am on Octopus Intelligent Go (I have an EV) so get 11:30pm to 5:30am at 7.5p per kWh.

I am not trying to heat to 60 degrees every day, it is only once per week, but is not completing and just keeps running until I force it to restart (this is my issue)

Does anybody have any ideas why it is not completing?

The tank is due to heat up (normal) between 3pm and 4pm, so if it gets hot enough, I will set it to run the disinfection afterwards.

The installer set it up to run at 4am initially, but I could do it in the afternoon if it works and take the hit on cost.

I have exactly the same issue with my system (Samsung, not Daikin) - it is never able to complete the legionella cycle and throws an error when it times out to say the legionella target temp (60C) was not reached.

The cause on my system is that my ASHP cuts out when the LWT hits 60C, meaning the hottest it will heat the DHW to is around 55C. The immersion also has a built in thermostat, and despite that being set to max, also cuts out at a tank temp of around 55C, so the legionella target temp of 60C can never be reached (56C is the highest DHW tank temp I've been able to observe).

Is there a menu option to set the disinfection temperature, or is it fixed at 60°C ?

NedS

FreeBear said:

NedS said:

rjmachin said:

I am on Octopus Intelligent Go (I have an EV) so get 11:30pm to 5:30am at 7.5p per kWh.

I am not trying to heat to 60 degrees every day, it is only once per week, but is not completing and just keeps running until I force it to restart (this is my issue)

Does anybody have any ideas why it is not completing?

The tank is due to heat up (normal) between 3pm and 4pm, so if it gets hot enough, I will set it to run the disinfection afterwards.

The installer set it up to run at 4am initially, but I could do it in the afternoon if it works and take the hit on cost.

I have exactly the same issue with my system (Samsung, not Daikin) - it is never able to complete the legionella cycle and throws an error when it times out to say the legionella target temp (60C) was not reached.

The cause on my system is that my ASHP cuts out when the LWT hits 60C, meaning the hottest it will heat the DHW to is around 55C. The immersion also has a built in thermostat, and despite that being set to max, also cuts out at a tank temp of around 55C, so the legionella target temp of 60C can never be reached (56C is the highest DHW tank temp I've been able to observe).

Is there a menu option to set the disinfection temperature, or is it fixed at 60°C ?

Yes, I can change (lower) it in my system, down to a minimum setting of 40C. Obviously, lowering it in my system would allow the legionella cycle to complete and avoid an error.

Hopefully the OP can identify if this is potentially the same issue they are experiencing.

astroL

I have a very similar heat pump.  The disinfection cycle kicks in under its own schedule (regardless of yours) and terminates when the 60C for ~30mins is complete.  Your water pressure is low at 1 bar.  Increase it to 1.5 - but most importantly - have you raised this problem with the installer?  Octopus installed ours and they seem reasonably quick to deal with problems.  Its *their* problem - don't make it yours!

Lawrence Harris