Hi Alister, I'm not entirely sure what you're asking here? The output from the GSHP (i.e. the temperature of the heating fluid flowing around your UFH) is controlled by the heat curve that you've set on the pump (I'm assuming that all GSHP's work on the heat curve principal like NIBE's - so apologies if this isn't the case. I'm only familiar with my NIBE S1255). The temperature should, indeed, fluctuate with outside temp variation - the colder outside the higher the output temperature. So to bring down the cost of usage you need to lower the output temperature. You'll have to experiment to find out how low you can go, whilst still heating the house to your target temperature. If you're already there, then I suspect the only answer is more insulation. I note that you say "the room it is situated in" - this sounds like a bit of red herring to me. If you've got just one room - in which the HP is installed - which is not achieving target temperature then yes, sure, you need to get that room weatherproof. But that's not going to greatly impact the overall cost of running the system if the rest of the house is weatherproof and well insulated.

Whilst with NIBE pumps it is possible to control them from a temp sensor (or even from your room thermostats) I've been led to believe that this is not the "right" way to control them - and that the method outlined above, using the heat curve, is the correct/best way to control them

Graham.

@graham-s thanks Graham, yes my query is slightly odd as the whole system is not properly installed yet. We are not living in the house full time yet as it is still under renovation.  I have dropped the offset by 6 degrees to keep the system running but not trying  to get an uninsulated room up to comfortable inside temperature, the rest of the house is toasty! My pump room will be insulated soon so the problem of excessive running costs will go away completely as the property is very well insulated.  I note your comments on thermostats, we have them for all seven UFH zones but they are not fitted yet. Every day is a school day with GSHPs so thanks for your help here. 

@alistersmith I think it is important to get some basic monitoring in place [if you don't have it yet].  You don't need fancy stuff, but at least flow and return temp.  If you can get flow rate, also good.  I am still on my monitoring journey, but just having flow temp was enough for me to spot when things were not good.  Such as this wobble when I reduced flow rate too much (to reduce pump noise).  I had a similar wobble when I reduced target temp too much.  (a PWM pump may fix that, will report back when I have one)  [Note:  The other dips are defrost cycles, it was -3 ish and quite foggy so I am ok with that]

Thanks, also got a S1255, been experimenting a bit with the offset ( we aren’t living there at present ) through MyUplink and managed to reduce consumption by 75% and still showing same internal temp. My flow return rates are early to mid 30 degrees and domestic hot water ( although not currently being used is similar to indoor climate supply/ return temps) . I will have running hot water from late feb so interesting to see how my consumption usage changes.  House is now thermally secure and insulated, so happier to experiment with temp settings and the joiner hasn’t complained of the cold! I plan to run the UFH constantly at low temp as it is fitted in all downstairs rooms, any experiences of this or does anyone use their pump periodically?

Hi, I'm another recent convert to a Nibe S1255 - had to replace a very old GSHP.  I do like it, much quieter and more efficient and great data feeds.....however, am now facing some strange issues with the heating coming on now the warm weather is starting to go!

My setup is a Nibe S1255, external hot water tank, underfloor heating with an external buffer tank. I am using the heat curve to manage my underfloor heating with individual temp controls in each room to open-close the relevant underfloor manifold not connected to the S1255.  I have no central temp control.

Domestic hot water heating is going very well, we have a large tank and it's topping up the heat to 48-50deg after use and a small top-up around every 5-6 hours, switching off when it gets to 50 every time.

However, with the heating something strange is going on.  As i am using the heat curve, I understand that the S1255 uses the Calculated Supply temperature to work out if heating is needed.

I currently have a calculated supply of around 29.2.  When the actual Supply Temp dips below 29.2 the GSHP starts to warm the underfloor heating circuit.  However, it never stops!  Just keeps getting hotter!

The flow motor is working fine and I have good flow through my underfloor heating with 2-3 manifolds fully open - I can see the warm water passing through the underfloor pipes (I have a temp gauge on each manifold).

What is the trigger to stop the heating?  My old GSHP would monitor the return temperature, and when that got to within 2-3deg of the supply temp it would stop warming the heating water.

With the Nibe there seems to be no such trigger.  And mine just keeps warming the water until it goes into error mode! saying 'Max temp through heat pump exceeded'.  It also goes way above the max temp of 47 which has been set in the heat curve. 

I think i am missing a setting or perhaps there is a fault with my S1255?

The attached graph shows what's happening - I actually had the minimum external temp set very low to stop the heating coming on due to this problem. So to get the data I put the minimum external temp back up again at around 8.50pm.  You can see the heating coming on, then the supply/return getting hotter and hotter.  I would have thought it would stop around 30-35 degrees?  Or are my flow/return not close enough (at end of graph the actual supply was 39.5 vs actual return of 37.8).  It's pretty much around 1.5-2 deg difference between supply & demand from 9pm onwards.

Any ideas appreciated!

Pete