Intermittent Raymarine ST6001 Autopilot

[aquacruise]

Hi, hoping someone might be able to help with the following. I've just bought a 2005 Fairline Targa 34 with Raymarine ST6001 autopilot and G series course computer (which is also interfaced to a Furuno Radar and chart plotter via SeaTalk).

The problem is, that after switching on the instruments, after about 20mins in standby the ST6001 head beeps and displays "NO PILOT". Pressing any buttons results in "SEATLK FAIL".

If you switch off everything for a few minutes (right back to battery switches) and then switch everything back on, it goes straight to "SEATLK FAIL".

Oddly though, if it is switched off for several hours or more and then rebooted, it works fine (until another 20mins or so passes by). Almost as though something is overheating??

However, if you actually use the autopilot (rather than leaving it in standby) then it seems to work fine. It's only after you leave it in standby again that the problem occurs.

I'd put up with it except that I've a 25 minute river run (which you can't use the pilot on) before I reach the sea, by which time I then can't use the pilot!

I've done the usual initial fixes. I've checked the SeaTalk wiring, I've swapped the order which the other instruments are daisy chained on the SeaTalk bus, and I've also swapped the SeaTalk ports around on the course computer (what I mean is that the course computer has two SeaTalk outputs/ports and I've tried the ST6001 on both, makes no difference).

I'm beginning to think it must be the ST6001 head, but one last thought is that is might be due to the Furuno system that is paralleled on the SeaTalk bus in case there is a compatibility issue?