Brilliant, Dave - the penny has just dropped for me! The units on the same housecode can be addressed either individually or in a sequence with another(s) then a function code can be applied which will operate those units previously addressed! Simple now but I had not grasped this concept - a 1000 thanks.

This probably explains the somewhat erratic nature of one of my lamps - I had probably not addressed it - as a beginner you tend to press buttons in an adhoc manner to try and get the blessed thing(s) to work - now that I know how the buttons work it's straight forward! I had previously downloaded several X-10 ccf's but couldn't figure out how they worked so I put all the lamp modules on A-1.

Paul