Cracked Firebricks

If you’ve had a wood burner or multi fuel stove for a decent period of time, chances are at some point you have experienced cracked firebricks. You may have wondered, What should I do?, Why have they cracked?  when to replace and, what your rights are regarding to warranty. In this article we attempt to address all these questions and provide advice on how to get the most out of your firebricks. The following is a guide only, if you are in any doubt, contact us or your local HETAS engineer for further advice.

Cracked Firebricks

A picture showing a new crack in a rear firebrick.

Introduction to Firebricks

During normal operation of your appliance, firebricks will experience heating and cooling. This results in thermal expansion and contraction. Sometimes minor cracks can occur. Hairline cracks can happen after repeated use or even in some cases upon first firing. When these minor cracks appear, there is no immediate cause for concern, and you can continue to use your appliance safely. Logically speaking, a small crack is no different to a join between two firebricks. Some manufacturers even supply larger bricks in two parts, pushed together.

A picture showing natural joins in a firebrick set.


When to replace Firebricks

  • If the crack exceeds 3mm in width. (Thickness of a pound coin)
  • When the surface of the brick has eroded more than 25% of the original thickness
  • When the brick begins to crumble or fall apart.


Caring for your Firebricks

To reduce the risk of cracks and to preserve their lifetime it is vital that firebricks are installed correctly and used appropriately. If you are unsure of how to fit your firebricks, please seek the services of a suitably qualified engineer.

Here are our top 3 recommendations.

  • Install correctly. If a brick is fitted too tightly it cannot expand under heating.
  • Build fires up gently to avoid thermal shock.
  • Take care when adding fuel. Do not throw logs or fuel against the bricks.



It is not uncommon for firebricks to crack. Provided it stays within the tolerances set out above this will not affect the safety or operation of your appliance. You may well find that the bricks continue to provide good service for many seasons to come – although this depends on the usage of the appliance and fuel. As these two variable factors determine the lifespan they are classed as consumable items. Manufacturers therefore will not cover firebricks under warranty.

See our other stove help topics >

Warranty on Stove Parts

How to replace rope seals on a woodburner door

Repairing Stove Doors

Stove Glass