A minor repair might be needed if your boiler is leaking, emitting unusual scents, or producing frozen condensate. Other symptoms of an impending repair include:
Low pressure, which could be due to a system leak or failed component.
If your boiler isn't producing hot water, you might have a broken thermostat or faulty valve.
A cold patch in your radiator could be a sign of debris buildup or sludge.
Noise that's accompanied by whistling could be caused by limescale buildup.
If your pilot light keeps turning itself off, there might be a problem with your gas supply. This is an urgent problem, so call for a repair straight away.