UPDATE Failing on value not in WHERE clause

Transact-SQL
1

Very new to SQL and relying on google but can't find a good reason why I am getting this error. Trying to update a record with a WHERE clause but I keep getting this error and the "QRT-S534" has nothing to do with my UPDATE statement.
Msg 245, Level 16, State 1, Line 1
Conversion failed when converting the varchar value ' QRT-S534' to data type int.

UPDATE SQL

UPDATE IM_ItemWarehouse
SET QuantityOnHand = 12
WHERE ItemCode = 25688
2

What data type is ItemCode column? If it's character data, then you have that ' QRT-S534' value in there somewhere.

3

Yes it is character data, but when I run other updates on other itemcodes they work, i.e MAX-30. Since MAX-30 is characters it executes the query ?

4 
UPDATE IM_ItemWarehouse
SET QuantityOnHand = 12
WHERE ItemCode = '25688' --<<--<<--