Cool heater passenger side

[thickman]

Hi all , yet another common fault , my zt190 , blowing cool on passenger side , I’ve taken out the matrix and descaled and flushed it out , put it back in and when cars up to temp , both pipes to matrix are red hot , with the heater fan off , so I assume the matrix is clear , but still when heating on , Luke warm on passengers side, is it always a 95% blocked matrix or something else , any help would be great full , as I don’t want anther 4 hours stuffed in the drivers footwell 😂