Hi , sorry to hear that your fire was capped off . this is always hard for the customer and the engineer , however that reading was very high and very dangerous .008 ppm is the borderline. Did the engineer attempt to find out the reason , ie, flue blocked , lack of ventilation damaged burner .if they didn't do this you could get another gas safe engineer to investigate. If the fire does need replacing ,there are plenty of models that would fit . your installer would go through this with you .
I have checked and parts can be had from heating parts direct.com
Thank you. I will try to get more investigations done into the cause.