UPDATE:

Engineer attended Friday last week to check the valve head on the unit... he took the top of the head off and it was all corroded inside.

We have worked out that there is a design issue with the outdoor unit, in that the valve head which has a hole in the top of head (not sure what for as all the others do) sits directly below the main header pipe inside the outdoor unit.

In cooling mode this pipe sweats with condensate which has been dripping down onto the valve head and draining through into the head corroding it and LG say this corrosion will have been changing the voltages so that the valve will not respond as it should as the signal will not be right

So he has swapped the valve head over with one of the working heads which has improved things but the coil is still getting warm on the affected unit... not as much so the fan stays running all the time but enough so that the fan stays on more than it should, which then zaps heat from the other coil.

Switch that coil off and the air off temp increases on the other unit that is calling for heat.

Hes going to come back out on the 19th to check the voltages on the head of the valve to see if its working properly.

Engineer is as keen as me to get this resolved and he agrees with me that the cowboys who fitted the system are out of business now for a reason. He said he has stuck with this since he came out first time because he could see that I knew what I was on about.

All the idiots who have been back to it in the past and have always fobbed me off with excuses despite me knowing what I am talking about.

As the main cause of the problem from day one seems to be a design issue then responsibility should fall with LG for all this has cost me.

The unit has warranty left on it till June next year but I bet theres not a cat in hells chance of me getting some money back on the repairs because it comes down to a design fault.

None of the other valve heads are affected as they are in another position away from the header pipe.