Boilers produce a combustion product called carbon monoxide, which is also called the silent killer. Carbon monoxide poisoning can cause symptoms such as dizziness, headaches, breathlessness and loss of consciousness. The milder symptoms can be mistaken for other common sicknesses. Therefore its very important you have your boiler tested regularly. Servicing will give you piece of mind that your safe, or highlight any issues before a boiler can be damaging to your health.