It is estimated that the average cost of a fireplace repair in Darien is around $122 to $1,721 depending on the extent of the damage to the fireplace. Cracks on the fireplace are usually caused by expansion and contraction of masonry joints due to changes in temperature. If left unattended, it can allow smoke and carbon monoxide to get in between walls. These cracks are usually found at the back of a fireplace and can be repaired by a basic mortar repair if found earlier. However, if the crack is already severe, it can cause structural damage to the walls of the house and can cost you $3,500 and up for repairs. If you already notice the formation of cracks, have them fixed immediately. It will only cost you $150 to $180 for the repairs. Another damage that can go hand in hand with a crack is water leakage. Water can go through cracks, and with the passing of time, it will allow mold to form and wood supports to decay. It can also make dampers rust and can ruin mortars and any wood near the fireplace. If the crack is along the roofline and flashings, it can cost you around $140 to $160 to have it repaired.