Hi. We have a Kingfisher Potterton boiler which works efficiently and is regularly serviced with the last one mid February. Soon after the service by British Gas we went away but left the gas heating on low. Soon after we returned we started to get a very musty smell from the boiler and I say it smells like fertiliser! British Gas have checked it twice and no gas leaks or carbon monoxide problems as we have two detectors in the kitchen where the boiler is. The smell occurs when the boiler is on and with or without the water on. The burner seal was changed but we still have the problem. Has anyone got any ideas please as to what has caused this smell?
Consider that the smell might not be from the boiler at all.
If the smell you detect has an ammonia or fishy pong then check the electrical fittings in the room - it's not unusual for the plastic of electrical fittings - ones that get warm like lamp holders for instance - it's not unusual for the chemicals in the plastic to break down over time and give off a strong smell.
Boiler cases are sealed units - so check the exhaust air outside the property - give it a good sniff. If you can detect the smell then it's a boiler issue - if you can't smell anything then it's something else that's causing it.
We may have found other answers which could help you.