A couple of things:

1. You should be running on weather compensation (WC) so that the FT reduces as the outdoor temp increases.  Your installer should have set this up!

2. The FT you need is determined by your emitters and your house loss and its best to run on weather compensation at the lowest possible FT consistent with keeping your house warm.  There is a procedure you can go through to adjust the WC settings, but its going to be difficult now the heating season is coming to an end.  In summary the procedure is

• set all TRVs and any thermostats to max.  Operate the heat pump 24*7
• make sure that the heat pump is running in pure weather compensation mode without any room influence
• slowly adjust down the weather compensation curve until the house only just gets warm enough.  Typically adjust be a degree every 24 hours
• You may need to balance the emitters if rooms land at different temperatures

Many leave it like this, operating on pure weather compensation.  depending on your house you may wish to set TRVs and any thermostat a couple of degrees above the desired temp in rooms that benefit from solar gain, so they act as temperature limiters.  Generally its best not to use TRVs or thermostats as temperature controllers (ie set them above the desired temperature not at the desired temperature thus allowing weather compensation to do its job in controlling temperature)

I stress that this adjustment is going to be tricky with current weather, but if you dont have WC running at all its worth putting in a basic setting like FT= 50C at OAT = -2 (or whatever the design temperature is in your location) FT= 27C at OAT=+16.

before you go any further however I suggest you read this introduction to heat pumps and be sure you are comfortable with the basics of how weather compensation works and post back with questions.  Suggest you read the heat pump manual section on weather compensation also so you understand the controls for this pump as they differ slightly from many others (generally in a good way!).

Many run DHW at 48, it will save a bot and generally will work fine.

Many thanks JamesPa - I will now go away and thoroughly read the Introduction to Heat Pumps. Hopefully I'll understand a little more to enable me to work out what, if anything, may need tweaking. The installer did fit and set up Weather Compensation but I didn't get time to question them on how it works, especially with all the other installations going on at the same time, including solar panels, inverters, batteries etc. Upstairs bedrooms are too warm first thing in the morning. The comfort temperature is set to 20C and setback to 18C. The radiators feel hotter now compared to when we had a gas boiler, Hence the question about reducing the heating flow temperature. We have turned down the flow using the TRV's which has helped a little. The thermostat is located downstairs in the coldest room (Lounge). During the evenings the comfort temperature just about keeps the lounge reasonably warm enough, but the bedrooms are too warm. It would be great if there was an option to have 2 comfort temperature periods. 20C for the lounge in the evenings and 18C for the bedrooms in the mornings.

Posted by: @tomdad

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The radiators feel hotter now compared to when we had a gas boiler,

That's a bit of a red flag.  I don't think your WC settings are correct.  No panic because the heating season is more or less over but some tweaks during now and during the early part of next season will likely save you 10-30% and increase comfort.  I will post again in next days but I do suggest to read the introduction.  

To get lower temps in bedrooms turn down the lockshield valves (the valves opposite the trvs).

Pages 59-62 in the Installation and Maintenance Manual describe the WC settings.  Its a bit cryptic at first but becomes clearer on subsequent readings and once you grasp the basics of heat pump operation which are described in the introduction.  I can clarify in subsequent posts.

I will post again.

@phil-s is this something you could potentially advise on?

I had a video call with Ideal Heating this morning and mentioned the above issues regarding radiators feeling hot. With their guidance the Heating Curve was adjusted from 1.5 to 1.3 and the Room Influence setting was changed from 50% to 20%. I will now try this out over a few days and report back here. The Heating Curve could be adjusted lower if needed but advised not to be less than 1.2

@tomdad

Here is some more detail.

Firstly your heat pump is capable of operating at 55 or 35 or anywhere in between and indeed for a bit either side.  Most efficient operation will occur when it operates at the lowest flow temp consistent with heating your house.  This of course changes with outdoor air temperature (OAT) which is why we use weather compensation.

The idea of weather compensation is based on the principle that the house energy loss is dependent on the difference between OAT and indoor air temperature (IAT).   Since, to first order, our aim is to keep the latter constant, this means that the main determinant of house loss is OAT, so if we vary the energy supplied to the house according to OAT we should be able to exactly balance house loss and energy supplied.  Furthermore because OAT is a 'leading' indicator of house loss, unlike IAT which is a 'rear view mirror' indicator, in principle control based on OAT is more stable (the precise explanation lies in a branch of engineering called control theory, but we don't need to worry too much about this).

It turns out in practice that WC works pretty well.  It has been used for boilers for many years in some countries.  We didn't adopt it in the UK, and as a result many of us have paid about 10% more for our gas heating than was necessary.  Operating at the lowest ft is also most comfortable, because thermal gradients are less.  We have also missed out on this with our boilers.

With a heat pump the efficiency gains from operating at low ft are even greater than with a gas boiler, so in almost all cases its the right thing to do.

The wc curve, ie the relationship between FT and OAT to achieve the desired match of energy supplied and energy lost,  depends on your house and the emitters (rads/ufh).  Installers typically set an approximate curve that's generally higher than the optimum, to ensure you don't get cold.  Thus there is generally room for turning it down. In your case there is a single parameter to adjust described in the manual I referred to previously.  Basically you turn this down until the house is only just warm enough.

Operating at lowest ft also implies in most cases operating 24x7, with all emitters open and without external controls.  Thus then leads directly to the process for adjusting the wc curve:

Turn all trvs and thermostats to maximum. Set the heating on 24x7 

Switch off room influence, in your case by setting the room influence factor to 1% (the minimum value)

Your system is now running purely on wc and will very likely overheat.

Now turn down the wc 1 step per day (you can start a bit faster but may have to go even slower as you approach optimum) until the house just heats to the desired temperature.

If the rooms are at different temperatures (or the temperature differences between rooms aren't wat you want), you may need to 'balance' the radiators by adjusting the lockshield valves (which are the valves opposite the trvs). Note that many lockshields only have any control when they are nearly closed.

Once your house just heats to the correct temperature and the room to room temperature differences are what you want, you have the optimum settings (or at worst the best starting point for small tweaks).  With a bit of luck these settings will keep the house comfortable whatever the weather.

From here you can, if you find it's necessary, set some trvs to a couple of degrees above the desired temperature to act as limiters and/or increase the room influence factor a but.  Many people find this isn't necessary and operating purely on wc gives excellent results, it's a but house dependent varying eg with solar gain.

You can also reinstate trvs as temperature controllers in a minority of rooms, however it's generally best to have as many as possible and certainly the majority fully open and balanced solely on the lockshield.

Your heat pump supports timed setback so if you want to reduce the house temperature by a couple of degrees eg at night then by all means do so using the controller, which will do this by reducing ft, ie in the most efficient way.

Finally setting up wc and balancing radiators is best done when it's cold outside, which isn't the case at present.  So expect to do a rough job now and tweak next season.

Hope that helps, feel free to ask for explanation of anything I didn't explain too well.

Many thanks JamesPa - that's great advice which is well explained and now easier to understand after reading more on the subject via your earlier link. I'll now continue my quest to optimise to system to provide the required comfort heating / optimal heat pump efficiency. This is a great forum - especially for newbies like me!

Hi JamesPa - I do have one more question please. I have 2 heating circuits, 1 circuit for upstairs and downstairs radiators, the other circuit for underfloor heating installed in an extension at the back of the house. The Heating Curve for the UFH is set to 0.8 and the Room Influence setting is 50%. UFH is on a constant temperature setting 24/7 and seems to be working well. Would you recommend any changes to these settings?

@tomdad 

How is it all connected/controlled.  The heat pump can only produce water at one temperature at any one time, so either it's all running at the same temperature or it's somehow mixed or time sliced.  Which of these?

2 x Halo thermostats 1 for CH & 1 for UFH.

2 x Motorised Control Valves 1 for CH 1 for UFH.

2 zone UFH manifold fitted with 2 x flow meters, and temperature control mixer which is set to max 50C

Posted by: @tomdad

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2 x Halo thermostats 1 for CH & 1 for UFH.

2 x Motorised Control Valves 1 for CH 1 for UFH.

2 zone UFH manifold fitted with 2 x flow meters, and temperature control mixer which is set to max 50C

Ok. When you say max 50 what changes it?  Does it in practice run at 50 and if so does the zone valve switch it on and off? 

Basically I'm trying to work out if you have scope to reduce the temperature of the ufh and just run at same temp as wherever the rads settle once you have adjusted the WC.