previously it was so noisy, it was like having a diesel tractor in the garden, rattling and thumping and hissing. I’d even had 2 disputes with the neighbour over it and to be honest I agreed with them. 
Now it’s just purring, god only knows what it was doing before but it’s chalk and cheese. Bloody electronics. 

Classic isn't it.  I will remember in future to suggest this to people experiencing odd errors.  Now I come to think of it a similar procedure was suggested when I had some errors with my Vaillant.  It turned out that the cause was a blocked filter so reset didn't fix it, but the fact it was suggested at all does indicate that it can be a problem.  Modern electronics eh!

Im glad you are now up and running.

@papahuhu Err, no I haven’t! I suspect that this may be linked with ‘Polling’ and perhaps @majordennisbloodnok may be able to throw more light on this situation. I suspect that as the comms for the heat pump are indicating a comms error, then no data is being passed to Homely - under this condition I suspect that the Homely algorithm is waiting for a status change but because it cannot ‘Poll’ the non functioning comms, it sits there awaiting a change in data. I may be talking absolute carp but the Major is far more clued up on modbussery than I. Me, I am just guessing!

@toodles, I'd have indulge a significant dose of guesswork, I'm afraid. 

It's not clear to me (largely through lack of familiarity with both Samsung units and Homely) whether the Samsung modbus interface draws its power from the outside unit or somewhere else. What @papahuhu posted suggests he believes it should take it from the outdoor unit and the Homely manual tends to imply this too, but it's also not clear what the Homely box is monitoring and what its LEDs are actually trying to say.

In the absence of a better understanding of the bits of kit, I'd say your explanation is as good a guess as any.

You wont need one in heaven either which, at least according to the calculation originally published in Applied Optics, is hotter than hell  (this has been around some time and the reference is trustworthy, albeit that the theology may not be!)