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.

What should I do?

So, you bought a new set of firebricks in the summer all ready for the Autumn. You go to add a log one October evening and you discover one of the bricks has a crack in it! What should you do? The first thing to do is not panic. This is not uncommon and is certainly nothing of immediate concern. Thinking logically, a crack in a firebrick is no different to a join between another firebrick. You may well find that brick goes on to give you a perfectly acceptable lifespan.

What you should do is simply monitor it. If the crack remains stable and does not expose more than say 3-4mm, then there isn’t really an issue. It is only when the brick will not stay in place, crumbles or exposes a significant area of the outer body do you need to replace. Some people will try and repair with fire cement. This has limited success.

A picture showing natural joins in a firebrick set.


Why have my firebricks cracked?

The majority of firebricks tend to be constructed from fired clay or vermiculite board. Clay tends to retain the heat, whereas vermiculite reflects the heat back into the stove. Other materials can include cast iron or Thermotte (a reinforced concrete), but for the purposes of this we’ll focus on clay and vermiculite. Whichever material you have, firebricks, like all internal components, are subject to thermal expansion. This is where the material expands and contract with extreme changes in temperature. A sudden or rapid change can lead to firebricks cracking. Similarly, heavy impact, incorrect fitting, poor fuel and loading can also cause a brick to break. Therefore, simple things like fitting the bricks correctly, loading the correct fuel gently and slowly building up a fire are all things you can do to protect them.


When to replace a firebrick?

If the cracked firebricks remain stable and do not expose the stove body, then there isn’t an urgent need to replace. If it is mid-season, it might be a good idea to have a replacement in hand. It is only when the brick will not stay in place, crumbles or exposes a significant area of the outer body do you need to replace.


Do firebricks have warranty? 

We have saved the most divisive question until last. At time of writing, I am not aware of a single manufacturer who will offer warranty on firebricks. Firebricks are exposed to a range of variables. Over such, neither the manufacturer or retailer have any control over. Firebricks are classed as a consumable item and are expected to be replaced over time as part of regular servicing. Even in the worst case scenario of bricks cracking on first lighting, they are, unfortunately, not covered under a warranty. Having said that, under normal circumstances, there shouldn’t be any reason why it cannot continue to be used in line with the above. Where bricks are mirrored you can reverse them 180 degrees or swap to evenly spread the wear.

See our other stove help topics >

Warranty on Stove Parts

How to replace rope seals on a woodburner door

Repairing Stove Doors

Stove Glass