Hotpoint Ultima DWF70 reporting AL03 but drain pump OK?

Hope someone can help with this one.

My DWF70 was reporting AL01 (leaking into the tray). Drained several times but mostly ignored (the joys of tennants!). Then developed hard fault of failing to drain and reporting AL03 (or poss AL05). Based on the info from this and other forums, I've basically got every panel off and done all the obvious:

Drain pump removed and stripped (all clean) and spins up on external power.

Pressure switch operates and tube is clear

Circulator motor spins free by hand (but not electrically tested)

Drain hose clear and no obvious obstructions in sump / filter housing

I think I've traced the original leak to a loose softener assembly where it screws into the base of the machine (now tightened); the tray is badly corroded due to long term standing water, which looks like it's got up to the circulator as the corrosion is on the motor core too - doesn't appear to have reached the windings though.

Behaviour now with all parts fully assembled: When running 12 min rinse cycle, small whirring noise (think it's the divertor moving based on covers open test?), but drain pump doesn't operate. Machine starts to fill, but circulator doesn't kick in as normal. Filling stops. Timer counts down as normal, but no circulation. At end of cycle, reports AL03. If same test is done with drain hose lower than sump, so that the fresh water drains through, then a pretty much immediate AL05 is reported.

With float switch, drain pump and solenoid connectors off - and starting the same 12 min cycle - there is never any voltage supplied to the drain pump (can't easily get to the circulator connections or would test those too). Is there any clever sensor that will do odd things without these connected though? Stops with H20 fault pretty much immediately due to solenoid being disabled, but assume the drain pump should still operate at start anyway? Or would empty sump disable that?

Based on the above, I'm thinking:
1) Circulator pump burnt out (or poss debris in it's hoses)
2) Timer / PCB fault
3) Wiring fault
4) Some sensor or other preventing the controller from energising the circulation or drain pumps.

I'm hoping for a simple one somewhere in number 4, 'cos all the others are expensive and awkward. Any and all advice welcome for what to do / try next.

Thanks,

Nomad.