Many people with heat pumps heat water only to say 48 with a weekly legionella cycle (often using the immersion) taking it to 60/65.  This should all be set up on the controller (look for a setting for legionella or disinfection). Heating to 60 every day significantly decrease efficiency and in most cases adds no utility.  You only need about 40C at the tap, any more feels too hot.

Depending on your dhw cylinder and spec of the heat pump 55 or 60 may well be unachievable.  It's certainly not desirable in most cases so unless there is a good reason to do otherwise I would eliminate the error and save yourself some money by reducing the set temperature to 48. 

I could go into more detail but if the obvious answer is ok that's in short the best way forward.

I think the NIBE uses both the ASHP and the element to reach the desired temperature, you need to make sure the element portion is working, you could have a defective element.

Periodic High-Temperature Cycles

NIBE systems feature a "periodic increase" function, which periodically raises the hot water temperature to prevent bacterial growth, such as Legionella. During these cycles, the system may activate the immersion heater to reach the necessary higher temperatures. Users can configure the frequency and temperature settings for these cycles through the system's control interface

Hi, thanks a lot for your answers!

To clarify: with 'periodic warm water increase' I actually refer to the legionella/desinfection mode running every 14 days, I do not plan to keep the warm water temperature at that level.

Alright, so it might be that the system is not designed for the heatpump to heat the water to 60 °C and the immersion heater (VB2210) should help in that case. But as far as I understand: the immersion heater is connected to the SMO20 as additional heater. Due to the current outside temperatures, the additional heater is not active (set to blocked on the controller). -> Do I need to disable any blocking of the additional heater? Actually I would like the additional heater to be only active when needed for the periodic increase and not any other time.

When would the immersion heater be active, is following understanding correct: The heatpump tries to heat up the water until the alarm limit at 60 °C. After failing, the immersion heater takes over until the desired water temperature is reached. Or is the immersion heater directly active from the beginning, supporting the heating?

Thanks a lot!

Ok.  The key point I think you have made is that the error only occurs only during the disinfection cycle.

That's getting quite deep into NIBE specific matters, IE how exactly the NIBE controller works.  It probably needs a NIBE expert/owner to answer that.  You could have a poke around in the settings/installer manual to see if anything pops up.

I apologise that I can't be more helpful on this occasion.

Posted by: @jamespa

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I apologise that I can't be more helpful on this occasion.

No worries, thanks a lot for thinking along 🙂

@tribol welcome to the forums. 

I’m just spitballing here, but from what you’ve described, it sounds like your system is hitting its BT12 (condenser out) temperature limit, which is what’s triggering the alarm 162 and shutting down the heat pump during the legionella cycle. This can point to insufficient heat dissipation… basically, the unit is generating heat faster than it can shift it into the hot water cylinder. That’s why BT12 climbs too high and the system trips out before hitting your DHW setpoint.

In theory, increasing the pump speed (more water circulating faster through the cylinder coil) can help by drawing heat away from the heat pump more effectively. If the pump slows down early in the cycle that could explain why BT12 starts to spike… the heat has nowhere to go.

I’ll flag this post with NIBE and see if they can help. 

In terms of legionella related risks, here’s some additional reading:

RENEWABLEHEATINGHUB.CO.UK "https://renewableheatinghub.co.uk/legionnaires-disease-home-hot-water-understanding-risks-and-prevention/"

Legionnaires' Prevention Tips | Renewable Heating Hub

Legionnaires' disease prevention: essential hot water temperature tips for safe, efficient homes.

@tribol here's an official reply from NIBE on your case: 

"Your legionella program is set to run on a weekly basis and will take your cylinder up to the default preset temperature of 55.0 degC and maintain it for a period of one hour, this will satisfy the legionella program. In your case the legionella program is failing because you aren’t reaching the default temperature of 55.0 on the hot water sensor BT6.

You should have a device called an HR10 (square grey box) on the front of the box is a rocker switch with on/off/auto, make sure this switch is set to “Auto” and you HW immersion has a live power supply. The best way to get help and advice from NIBE is to contact Homeowner Care on 0330 311 2201."