Stop and call someone today if
These are safety issues, not maintenance ones. Don't wait, and don't have a go yourself.
- You can smell gas. Leave the property, don't touch any switches, and ring the National Gas Emergency Service on 0800 111 999
- A yellow or orange flame where there should be a crisp blue one
- Black or sooty marks around the boiler casing
- A carbon monoxide alarm going off
- Headaches, dizziness or nausea that clear up when you leave the house
Carbon monoxide has no smell. If there's no CO alarm near your boiler, that's the cheapest thing you'll buy all year.
Signs it's on its way out
None of these is fatal on its own. Two or three together usually means the sums have stopped working.
- Past about twelve to fifteen years old, and parts getting harder to source
- Two or more repairs in the last couple of years
- A repair quote that's a decent fraction of a replacement
- Radiators taking noticeably longer to warm through than they used to
- Banging, kettling or gurgling that comes back after a service
- Losing pressure over and over with no visible leak
- Hot water running lukewarm before it runs hot
The honest arithmetic
A repair on a nine-year-old boiler with a decent service history is money well spent. The same repair on a seventeen-year-old boiler that's already had a pump and a diverter valve is money spent twice.
The question worth putting to any engineer isn't "should I replace it", because eventually they'll all say yes. Ask what's likely to fail next and what that one will cost. A good engineer can answer that for your specific model, and the answer tells you what to do.