MagnaFlow causing F1 & F4 ignition faults or coincidence?

I have a Glow Work Flexicom 35 cx and it's worked brilliantly since it was installed in 2009. Last week I had the annual boiler service with British Gas and the engineer also installed a Magnaflow for £235. Since then I've had at least eight F1 and F4 ignition faults on the boiler and no hot water/heater until I press the reset button.
Is this a coincidence or does the Magnaflow affect the ignition process?
Should I have the MagnaFlow taken off??