What are the weather compensation settings ? Are you sure the system runs according to these settings ?

Are there internal thermostats at low temperatures that stop the system ? because these operate alongside the WC curve, as an upper limit.

Posted by: @pash44pump

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External pipework is 90mm

I very much doubt that! I am talking about the primary pipework to and from the heat pump, inside the inadequate black insulation. In a 'normal' installation, it will often be 28mm (OD, outside diameter) copper pipe. If you have a pair of calipers, measure the OD, if not improvise something to do the measurement eg dividers or a drawing compass.

While we're on the primary pipework, this photo you posted is rather intriguing - it doesn't even look like copper, more like clear plastic pipe with diagonal reinforcement!

@tasos There are room thermostats which call for heat from the system. As to whether the system runs according to the WC settings (which are recently added), I don't know yet.

My priority at the moment, is understanding the design of my system, whether it accords to scope and relevant standards and is fit for purpose based on my property. Once I have established that and contacted the installers to start the process of any remedial works, then I will start looking at how exactly the system is running and what to do to improve it via various settings. 

Thanks

Posted by: @pash44pump

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My priority at the moment, is understanding the design of my system, whether it accords to scope and relevant standards and is fit for purpose based on my property.

Agreed. The WC and thermostat settings only become relevant when the system is running, which can't that far away now, but we haven't got there yet.

The two current questions are:

(1) OD (and material) of the primary pipework?

(2) is there a formal heat loss survey calculation, and if there is, what does it show? 

@pash44pump I don't know the procedures in UK, but in Greece every property has an energy certificate, which is the starting point for heating/cooling considerations. These are provided by certified energy engineers. Is there something similar in UK ? Because that should be my starting point in your investigation.

Then you should proceed at checking whether the design meets the requirements.

And finally check whether the installation and operation is according to design.

@cathoderay of course it's 28mm diameter  🤣 I measured the circumference and didn't do the conversion. Glad someone is awake.

I've attached 2 more photos of the offending pipework, which runs from the heat pump to the isolation valves

Posted by: @cathoderay

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While we're on the primary pipework, this photo you posted is rather intriguing - it doesn't even look like copper, more like clear plastic pipe with diagonal reinforcement!=

So that's the flexible rubber pipe which connects to the back of the external heat pump.
We're looking at the outer stainless steel braid.

The insulation has been arranged so as to channel rainwater into the gap between insulation and pipe.
From there it absorbs the heat and throws it around the base of the heat-pump to keep its feet warm in winter. 🤨 

Returning to the set of 14 photos on the previous page, can someone else please clarify that Pic.1 is of the Domestic Hot Water (DHW) tank
and Pic.2 is a buffer tank in a different location?

The drips of solder-flux, copper salts and rust residue on the pipes and valves tell me a lot about the standard of work which has gone into this.

Are any of those areas actually leaking?
Or is this just debris left after the installer had 'finished' the job?

I have so much more to write on this, but unlikely to get back to it until tomorrow.

@pash44pump I don't think piping is the problem (though it may increase running cost). Your pump should be able to deliver max outflow temperature of 60C at -1C outside temperature. This should be more than enough for the UFH. As far as the radiators are concerned, it depends on the radiators. I suppose they are designed for your old oil-fired system, so they may not be adequate. In any, case I would not turn them on, if no one lives there.

All in all, I would bet on the system not being operated properly. Of course for optimal operation, other things could be investigated. 

Posted by: @transparent

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So that's the flexible rubber pipe which connects to the back of the external heat pump.
We're looking at the outer stainless steel braid.

Yes, I see that now, but I wonder what its internal diameter is? A very short length may not matter that much, but longer lengths may impede flow. My line of thinking was that if the primary pipework is in some way insufficient, then it will never be able to transfer enough heat. At least we know that some of the primary pipework is 28mm copper, thanks @pash44pump for that.

For now, I think the key thing is to establish whether there was a formal heat loss calculation or not. If there was, what does it show? If there wasn't, then Sustain Heating and Renewables may find they are in a rather unsutainable position. Let's hope they did do one. 

@pash4pump 

Ive looked at the photos and would comment as follows:

The internal insulation seems better than the external, I can see a couple of untaped corners which should be redone but I doubt this is a major issue.  My view is that the external insulation should be stripped off and replaced in its entirety.

Internal cabling is a bit of a mess, Im sorry but having suspended cabling as shown in photo 1, unsecured either end, is just slopy in the extreme.  Cable ties and cable clips are both easily available to do a proper job.

I cant see any antifreeze valves, but they are often difficult to spot.  There should be either a pair of antifreeze valves (the ends of which should NOT be insulated) near the heat pump or the system should be filled with a glycol/water mix, with a strong preference for the first of these.  I would check.  

Im presuming that the buffer tank is shown in the second photo and the DHW tank in the first. 

If Im right then the buffer tank is too small to give adequate stratification (even if it were properly controlled) and thus mixing is inevitable.  Given that the load is dominated by the UFH running, presumably, at 35C you potentially have return water from the UFH at 30C mixing with flow water at 50C significantly diluting the flow temperature of the water to the emitters.  This is an efficiency nightmare and is hardly going to help performance.  I would love to see the design calculations for this side of the for the system, but doubt there are any.  My guess is that the installer decided to 'fit a buffer tank so that he didn't have to bother worrying about the existing system', except that he was wrong in thinking that.

The scope document looks fairly comprehensive to me, more than I got in some respects, but it doesn't contain much by the way of design calculations.  It would help diagnosis if you could tell us where the heat pump and cylinder are on the plan and which rooms are the coldest.  Also at what temperature does it become inadequate and by how much?

My strong suspicion (little more than an educated guess based on what we know so far) is that you have a significant drop in temperature between heat pump and UFH pipework due to the combination of buffer tank, long pipework and pipework with poor insulation and the mixing valves, exacerbated by not having the rads on upstairs and the interaction with room thermostats which probably turn off flow to sections of UFH when it should be on.  As a result the UFH is not receiving water constantly at the design temperature, causing your shortfall.  Its also possible that the flow rate through the UFH is insufficient, leading to a higher DT than ideal, reducing the average temperature and thus heat transfer from UFH pipes to screed.  With the boiler, running at perhaps 55-75C, some of this would still have happened but been masked because of the high starting temperature.  

Some temperature measurements combined with neutralising the external controls by turning them to max, will confirm or deny my suspicion, but of course only once we get to the heating season.

To help with diagnosis it might be worth finding out how the UFH controls and heat pump controls are connected (if indeed they are).  A common way to do things when there is a buffer is not to connect them, which for the installer has the advantage that they don't have to touch the existing control system.  In this arrangement the call for heat derived from the room thermostats turns the UFH pump(s) on/off drawing warm water from the buffer tank and replacing it with cool.  Totally separately the heat pump monitors the buffer tank temperature and tops it up when it goes below a certain value.  If it is wired like this then it explains your summer behaviour.

Hope that helps

Referring to an early point, night time firing could be caused by legionella precautions, could it not?