Note the boiler make and model, the exact error message and whether the problem affects heating, hot water or both. Explain when it started and whether it happens all the time or only at particular points.
Do not remove the casing or attempt work on gas components. If you suspect a gas leak or carbon monoxide problem, use the official emergency guidance rather than waiting for an online enquiry.
A repair may depend on diagnosis and parts availability. If replacement is worth considering, ask for the reasons and compare the scope of both options before deciding.