@toodles worth giving that an inspection?

@netdonkey Usually, this chamber will collect a thin black film of very fine particles and unlikely to impede the flow to any degree, however, having said that, it wouldn’t harm to clean it out but make sure you isolate by closing the valves on either side of the ‘magna clean’ chamber first! Regards, Toodles.

@netdonkey definitely give that a clean, following what toodles said, and tell us if it helped.

@netdonkey Do you feel confident to check the filter, you should be able to isolate the valve ether side and normally open a drain on the bottom of the filter to confirm the pressure is gone, then you can unscrew the lid to clean it out, be aware some of these filters are fitted with a magnet and a spring inside, this will need to be assembled back as it was after cleaning.

The code for the fault is low water flow so best to investigate if it is restricted or air locked. 

Do you know what the water pressure is in the system? 

@ashp-bobba reasonably confident to have a look at it.  The current system pressure is 1.7bar which from googling seems ok.

@netdonkey agreed, sounds ok pressure.

Quick question I just thought of, can you take a picture of the flow sensor assuming the engineers fitted it to the return pipe to the condenser, I remember Samsung explaining to me that this sensor only works in 2 orientations and that there are restrictions, for example (and I am tying to remember a year ago now) it must be flow up and have something like 100mm before the sensor and 300mm after before any fittings to prevent turbulence or air bubbles and prevent it from miss reading, or horizontal with similar restrictions. 

Just trying to rule a few things out.

@ashp-bobba pics attached.

Flow direction indicator in it points upwards

@netdonkey Ok, that looks correct to me and a nice amount of pipework above the sensor. 

Does the system fail on flow when heating the water as well or is it just when on heating? Are you able to check what the flow rate is when on hot water?

Let me know how you get on cleaning the in line filter. 

@ashp-bobba It trips on both but more frequently with DHW.  Re the flow rate when ion DHW, I think its the same FSV but will have a look

@netdonkey Ok. Can you give me the model and serial of the cylinder so I can work out the ports, I cant quite see the badge and different manufacturers use different ways for the bottom mounted buffers which this look like, I am not sure if I am placing the flows the correct way round. 

Pink is ASHP flow

Blue is ASHP return

Red Buffer F/R

Orange DHW F/R

Green Circle (assumed heating pump and connections)

Oh great!
We now have someone else here who can doodle on top of photos  

Can I please check @ashp-bobba that my arrow is pointing to the flow sensor which you've been discussing with @netdonkey ?

And I've turned on the light in the cupboard so we can more easily see the black component parts in the gloom.

Net Donkey - you might want to ask Santa for some pipe lagging with a wide bore to insulate around those brass valves.

Any pipes and metalwork within 1-mtr of the cylinder will be sucking heat out of it...
... even the pressure-relief valve and down-pipe on the right, which doesn't have water in it.

BES sell a good range of Kaiflex Class-O insulation with bores up to 54mm.

Glue the slit-sides back together with Impact Adhesive.... the sort you leave to dry on each half before pressing them together.

@transparent Hello, yes thats correct or at least it appears to look like it, this is the flow sensor that needs to be on the return pipe back to the ASHP condenser and is the little 5 wired bit of magic that causes all them errors when there is a lack of flow

I thought adding arrows to the picture may help as I was trying to work out which part of the circuit was doing what, something was not looking quite correct but I didnt want to work it out until I can see the cylinder diagram and confirmed the location identity of all ports on that multi port cylinder.