A lot of landlords write off ECO4 the moment they realise their tenant doesn't claim a qualifying benefit like Universal Credit or Pension Credit. That's only half the picture. Every metropolitan borough in England and Wales can, in principle, run its own "flexible eligibility" route into ECO4 alongside the national benefits route — a route usually shortened to LA Flex.
Birmingham publishes a Statement of Intent for LA Flex, which means a household in a Birmingham rental can be referred onto ECO4 using the council's own criteria (typically income, health, or fuel-poverty triggers) instead of the standard benefits test. If your tenant's household income is modest but they don't tick the Universal Credit box, that's exactly the gap LA Flex exists to close.
Birmingham sits inside a dense private rental market where a small portfolio of terraced or period stock is typical. Each of those properties is assessed individually against Birmingham's criteria, not as a portfolio, so a landlord can easily have one qualifying property and one that doesn't in the same street.