Keep out the birds and the rain.
We lose count of the number of chimneys we attend in the spring. The fire is off for a few days as you enjoy the unseasonably warm weather of April. 3 days later it is bitterly cold again and you try to light the fire. Only you can't! A jackdaw has built a nest in it, knowing that he is protected by the Wildlife and Country Act 1981 and you aren't going to be successful with eviction until August! Prevention is better than cure!
Rain in chimneys is now more of an issue than it used to be with the growing popularity of manufactured 'ovoid' coal. The high sulphur content in these and moisture in a chimney combining to produce sulphuric acid. We have seen numerous chimneys and liners destroyed by this. Fit a cowl and keep the moisture out!
Priced at £85 for supply and fit of stainless steel bird guard