Once properly installed, biomass systems are generally very reliable provided they are regularly serviced and maintained. Typically you can expect the greatest lifespan from a boiler that has been taken care of (20+ years).
To take care of your boiler properly you will need to regularly clean it (rake out the ash) and get it serviced annually by a trained engineer. A reputable company will provide you with training on how to maintain your boiler, during installation or servicing. As well as extending the boilers life, regular servicing helps prevent breakdowns, which are costly if you have to use fossil fuel for heating when the system is down. Additionally, it can help prevent parts breaking, which may be costly to replace. It is equally important for ensuring the boiler continues to run at peak efficiency, so you get the maximum heat possible from the fuel being burnt.