Your chimney sweep can supply and fit cut to size replacement fire bricks. (flat brick only)
The firebricks in a stove reflect heat back into the fire which allows for a hotter, cleaner burn but these are wear items and will need replacement from time to time.

Example 1

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If a brick is well supported on three edges then it can remain in place.

Example 2

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As a general rule a single hairline crack is not a problem.

Example 3

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Replace if it looks like it could fall into the fire.

Example 4

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Replace if you can see the stove wall behind.

We can fit replacement  firebricks, supplied by you, free of charge, after sweeping.

Wood burning - sweep every 3 months in use.
Smokeless - sweep every year.
Coal - Never burn coal in a stove with a liner.