Do you have the user manual? If not you can download it from https://www.nibe.eu/en-gb/assets/documents/8307/231759-1.pdf. If link doesn't work, just google it. In there you will find instructions about scheduling, though they are not necessarily easy to follow!! It depends on your particular set up e.g. floor sensors or not. We don't turn our heating off overnight but once we were doing it as an experiment and the installer had to help us. I seem to remember it was something to do with putting in the times and the temperature at which you allowed the heating to start, so he set ours to -10C!! I know, sounds crazy. Water heating is set separately and is easier to set up. 

It sounds as though the heating is coming on overnight because it is set to work on weather compensation. During the day the temperature will be high enough for the heating not to come on but during the night as the temperature drops the heating kicks in. You can switch the heating off altogether. See page 40 in the manual - Menu 4.2 - Operating Mode. The default is Auto but you can change it to Manual and then deselect 'heating'. This allows the system just to heat water as required. 

However, it's probably more important to work out what is causing the humming noise as during the winter you will probably want to keep the heating on overnight, especially if you have underfloor heating. You will hear the mantra 'low and slow' i.e. run heating at lower temperatures constantly. (As an aside, once we mastered that approach our heating bills went down.)

When the heating comes on it could be the pump that is humming. How many pumps do you have? I have no understanding of how to deal with noisy pumps but there are many of this forum who will be able to advise as it probably doesn't matter which ASHP make you have.

I hope this helps.

Welcome to the forums @superduck 

Looking at the manual @lizzie provided you can do the scheduling you're after – see below. But as Lizzie has stated, it's fine to do that at this time of year, but this isn't a solution going into the winter, so I'd recommend you try and identify where the reverberations are coming from and sort that out.

Tp address your immediate questions, you can program your NIBE SMO 20 system to avoid running during the night between 21:00 and 07:00 while still ensuring you have hot water in the morning.

1. Scheduling Hot Water:

• Go to Menu 2.3, “Scheduling Hot Water.”

• You can schedule two different periods per day. For instance, you can set a schedule to ensure hot water is ready before 21:00.

• Select “activated” to enable the scheduling and set the desired times for hot water production.

2. Silent Mode:

• To reduce noise during the night, you can schedule the compressor to operate in “Quiet Mode.” Go to Menu 4.9.6, “Schedule Silent Mode.”

• Activate the scheduling and set the quiet mode to run during the hours you wish to minimize noise, such as from 21:00 to 07:00.

3. Blocking Additional Heat:

• If needed, you can also block additional heat to ensure the system doesn’t come on during the night. This can be done in Menu 4.9.5, “Schedule Blocking.”

@editor Thanks Mars for coming in on this. I tend to lurk rather than participate and have learned a lot from the forum. However, there doesn't appear to be many NIBE owners to provide support so I felt I should make an effort even though my expertise and knowledge is limited.

Just a comment on additional heat. As I understand it, additional heat operates only when the ASHP is supplemented by another source of heating (electric/oil/gas) and the ASHP isn't sufficient to meet requirements. The main purpose of it would be to use an immersion heater for the periodic hot water increases to prevent bacterial growth, which should be scheduled. I don't think that should be coming on except for that purpose.

Thank you so much for your detailed replies - much appreciated.

The humming noise seems to be most noisy in the pipes in the skirting boards but it starts in the boiler room - it has now been happening for 2 days solid which suggests it’s not part of the system warming water.  It sounds like air/water rushing?

@superduck I can sympathise as I find low level humming noises disturbing too. This sounds like it is something to do with the way the system has been installed. I have no expertise in plumbing and heating installations but hopefully someone who does will pick this up and ask the right questions to help you track it down.

@editor Mars, could you possibly tag some members who can help with this? Thanks. Lizzie.

Posted by: @superduck

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Thank you so much for your detailed replies - much appreciated.

The humming noise seems to be most noisy in the pipes in the skirting boards but it starts in the boiler room - it has now been happening for 2 days solid which suggests it’s not part of the system warming water.  It sounds like air/water rushing?

I would suggest that you start by bleeding the radiators and topping up the system.

Is the humming continuous or is it only when the water pump is running?

Posted by: @lizzie

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@editor Mars, could you possibly tag some members who can help with this? Thanks. Lizzie.

I may have to refer this off our website to where I interact more with installers. Had a few days off with family, and will be on the case this week.

Thank you so much everyone for your help with this.

the system was set at 18 degrees to kick in, so at night it would start and then create the humming in the pipes in the bedroom - so we changed the temperature to 10 degrees and the sound has stopped and we can sleep again! So the system is working normally, we might just have to open some valves on the radiators to see if the noise lessens when the temperature drops at night 

@superduck

I am pleased that you can once more sleep.

I would suggest that you should now try to identify the root cause of the noise, so that it may be possible to rectify the problem before the heating season starts.

If, as you say, the noise appears to emanating from the pipework, then it could be one of several causes. Pipes don't vibrate and emit sound by themselves, so there must be another cause.

Is the water pump speed too high? This can cause vibration and noise in the pipework.

Is there any air within the system? Have the radiators been bled?

Is the water pump correctly installed? Has the pump been left hanging on the pipework or mounted securely? Where is the water pump located?