How old is it, and are parts still made?
Age matters less than parts availability. A well-maintained older boiler with readily available components can be the rational choice; a newer one whose manufacturer has discontinued the parts is not.
Is it the boiler or the system around it?
Cold radiators, poor hot water and noisy operation are often caused by sludge, imbalanced radiators or faulty controls rather than the boiler itself. Replacing the appliance without cleaning the system just gives you a new boiler on top of an old problem.
How often has it failed?
One breakdown in ten years is a repair. Three breakdowns in two winters is a pattern, and the cost of repeated emergency call-outs and lost hot water starts to rival the price difference between repair and replacement.
What is the efficiency of what you have?
Older non-condensing boilers waste a substantial share of the gas they burn. That gap is what you pay for every month, not just on installation day.
What does the rest of the plan look like?
If insulation or a heat pump is on the horizon, the boiler decision should fit that sequence rather than pre-empt it. Sometimes the right answer is a repair now and a bigger conversation next year.
This guide explains how the work is normally approached. What your property needs depends on its construction, condition and existing systems — a survey is the only way to know for certain.