Two questions:
- has your son repeated a year before?
- did he study in higher education before he began his current course?
If the answer to both those questions is 'no' then he should still have his 'gift year' or his '+1' year of funding left.
As others explained above, students are eligible for funding for the duration of their course plus one 'gift/spare/+1' year. If your son studied, for example, Yr 1, Yr 2 and Yr 3 and now just needs to repeat Yr 3 then he should be fine.
The rule only applies to the Tuition Fee Loan, you can be confident he'll be eligible for a Maintenance Loan regardless. If he has run out of Tuition Fee Loan entitlement because of previous study (he's already had a repeat year or he studied in higher education before starting his current course) then he will need to submit evidence of 'compelling personal reasons' (often referred to as CPR) to request an extra year of Tuition Fee Loan funding. CPR is typically for health reasons (physical and mental health), bereavement or caring responsibilities.
Starting an academic year without funding in place does mean accepting that if no Tuition Fee Loan is ever approved, he'll be liable to pay the fee himself. After the first two weeks back, he'll become liable for 25% of the annual fee but most universities won't ask him to make a payment, they'll give him a chance to secure the Loan. His fee liability won't increase until January (at which point it goes up to 50%).
In the meantime, if he's struggling to pay living costs, he can probably apply to his University's hardship fund which may make non-repayable grants.
And, finally, his online student finance account may struggle to understand that he needs to repeat a year (it 'thinks' he already finished his course). If there's a problem applying online, the paper form is available here:
https://www.gov.uk/student-finance-forms/y/studying-full-time-and-qualify-for-a-tuition-fee-loan-and-a-maintenance-loan-full-support/apply-for-student-loans-and-grants/2025-to-2026/yes
Good luck!