Really appreciating your input here.... let me know if you ever have a problem with any automated gate system, I might be able to return the favour!
I'll sit down later and try just what you have said. I agree with you about the sensors, I needed to rule out any work the previous owner did, so I have already replaced the sensors with the correct type. However I might just double check they were the right ones, because you're right, I just ordered a new pair using the same part code.