Fuel starvation (403)

[UHT405]

Could well be fuel starvation as others have suggesrted (I've had that happen too) but don't forget the condenser - a weak condenser can give exactly similar effects, the engine will start (sometimes) but the condenser breaks down when the engine is under load, shorting out the LT electrics. It's an easy one to check out, just in case.....

Good luck - these things can be very frustrating to get to the bottom of....!