IVT HT Plus E7 - what happens next?

frslam

back in 2009, I ordered a GSHP for a New Build House. I ordered from Ice Energy who spec'd  6kw HT+ E6. My new build house is 160m2 over 2 floors, ufh on both floors. I told them I wanted to extend in the future so they up'd the spec to 7kw. I dug 2 x 50m trenches for 200m of pipe in each trench as per their plans - trenches are maybe 6 or 7 metres apart. Ice Energy knew these systems have electric heater back up. Am I right in assuming the new heat pumps no longer have electrical cassette back up? My SAP says the space heating requirement of my house is 7,411 kWh/year. My Building Warrant had an oil fired boiler and radiators as primary heat source but I upgraded to a gshp/ufh without telling them. If my heat pump is on the way out, do I have to change to Air Source if I don't want to add more ground collector pipe or are there any companies who cater for legacy installations? If I had enough collector to cater for a 6/7kw gshp (albeit with electric cassette backup), and with advances in tech over the last 14-15 years, could anyone guestimate whether I had enough collector to run one of the newer 7 or 8kw gshp's? Ta