any updates in this mild spell are you boiling indoors yet?

Thanks for asking. Yes, the indoor air temperature has certainly been more consistent, a bit higher by a degree or two despite the fact I have lowered the leaving water temperature by a few degrees. The Mark 1 Human Sensor (me) also reports good comfort levels. All in all a success, and I don't think my costs have increased greatly, if at all, the lower LWT appears, as expected, to mean better performance, with COPs at times in the 4-5 range. Sometimes I think we forget how much difference a change in COP can make. For example, a seemingly not very large change, at least in absolute terms, from a COP of 3 to 4.5 means, all other things being equal, including having the same heating load, the unit costs part of my electricity bill falls by one third - where I would have paid £100, I now only pay £66.66, not a trivial saving. 

Here's my chart for the last week. On Monday, I restarted the overnight setback (using room stat down to 16 degrees between 2100 and 0300), as I am interested to see how the now all valves open system copes with the recovery period after the setback. Previously it struggled, sometimes taking 12 hours or so to get back to temperature. On Tuesday morning, after a mild night, it recovered well, back to where it should be by 0700. Last night was significantly colder, and the recovery has been a bit slower, but by no means a disaster, despite being in defrost territory. Bear in mind this is partly managed by my auto-adapt script, which adjusts the LWT depending on how far the actual IAT deviates from the desired IAT. At the moment the script is set up to do one degree of LWT change for every degree of actual vs desired IAT deviation, up to a max of 3 degrees eg if desired IAT is 19, actual IAT is 17, deviation is 2 degrees and LWT increases by 2 degrees. These parameters are easily changed, by editing the script and restarting it. I am going to run the system as is for a week, and then see if it needs any tweaking. 

Note: subsequent comments here about setback running have now been moved to another thread here.

Truly heat pumps are a miracle, that surpasseth all understanding...    

Somehow that feels like the basis of a motto/strapline. 

Without a doubt the combination of the nonlinear response to the main variables, the inherent complexity of the thermal dynamics of houses, contrasted with the extremely simplicity of the thermodynamics on which it is all based, really does make them fascinating beasts.

Can you go lower?

Very possibly. The IAT is at the warm end of my preferred range, and it looks like we'll have fairly settled though cool weather here over the next few days so a good time to experiment. Watch this space... 

I dropped the weather compensation curve

That'll do it ;)

Can you go lower?

Bob

Truly heat pumps are a miracle, that surpasseth all understanding...    

I've just remembered...two days after I opened the LSVs I dropped the weather compensation curve 2 degrees, and then 2 days later I dropped it by another 2 degreees. 

Interestingly, no obvious penalty, in fact very possibly (need more data, and there are things I haven't controlled for...) an improvement! In both charts the mean room temp improves a bit (as expected) and in both charts the energy in appears to fall. It's more marked at 5 degrees than 2 degrees OAT, but still present on both charts. Truly heat pumps are a miracle, that surpasseth all understanding...    

Swapping the radiator for a fan coil might not give you additional heat output because it's not the radiator that's causing the "restriction".

Absolutely, I am very aware of that! Moving to a fan coil is an (major) aesthetic improvement, but only once I know it will have adequate flow.

I am still trying to think of a way of making a diagnosis ie where is the obstruction, and what is it. I know how to drain the system and so also know it is not a trivial undertaking, and I would prefer to know if possible what I need to fix while it is drained down. I am also not inclined to do it during one of the coldest month's of the year, in case something goes wrong!  

Bob

I may need to check the flow rate though!

Shouldn't be a problem, in common with many fancoils it has a very short pipe with lots of fins on, not a long pipe.  That means it doesn't add much to system volume or resistance.

At full output expect to hear the fan quite distinctly (but not annoyingly, at least not to me).  Mine rarely goes up to full speed. 

One thing to watch is that it shuts down when the FT < 30C.  So far this hasn't been a problem, but at the end of the season it might be as I might end up operating at a FT just a bit under.  This setting isn't adjustable, but Im guessing a resistor in series (or parallel as appropriate) with the sensor might fool it into thinking the FT is just a bit higher than it is.  I might have to make it switchable summer/winter if I use the unit for cooling, which I just may.  That said the room where it is has another radiator and gets lots of solar gain, so it might not matter when we get to that point in the season where Im still heating but at a low FT.