I'm Having a problem with a Sanyo R410A VRF system.

I hope somebody can throw some ideas my way before i start pulling out the gas.

22 fan coils when in heating, all display the standby heat symbol and a little heat reaches the coil but not enough for the unit to start heating.

Meanwhile, the condensing units start up, the inverter comp, and the fixed comp's start running, the discharge pressure runs around 25-29 bar, suction around 5-6 bar, the discharge pipe was getting too hot to hold,
but within 10 minutes, everything winds down untill it stops altogether.
5 minutes later the cycle starts over.

When i run only half the system, the standby symbol comes off, the units run with poor heating but condenser still cuts out after 10 mins.

Pipework not crossed, checked correct valve opens in all SV boxes, tried a power reset, even tried adding a couple of kilos of gas but makes no difference.