I have not heard of the company Solar Air UK, so cannot comment, but there customer service skills does seem to lacking here.
It is common for a 10 year warranty as standard on inverters, but this does depend on the manufacturer and I do believe extended warranties can be bought too.
A RECC and MCS accredited installer has to give an Insurance Back Warranty for a period of ten year. So again, should the installer cease to trade, then you have the insurance backed warranty to fall back on.
I’m happy to report that the MCS certificate will include from the 5th November 2015 the warranty information that is now required for domestic properties having solar PV installed. This will give you an extra level of security and peace of mind for your new inverter once its eventually installed.
It’s all down to terms and conditions that you sign up to, but the manufacturers warranty doesn’t include installation costs, but as they seem to have failed on the ‘customer service’ aspect, I would recommend waivering such costs as a gesture of good will at this time.
Keep us updated here and perhaps send them a link to this ongoing forum.