I'd say the pump is knackered and will need replacing.
No matter what the system pressure unless the pump is circulating the water the flow switch will not operate allowing the boiler to fire.
If you can't find a service agent for Baxi, either ring your nearest Heatmerchants (the are Baxi agents) or ring baxi dorectly and they will give you a number of someone to help
T
June 2008