X-10 drivers in parallel?

[SonomaRoBo]

I'm trying to have two different X-10 devices provide power to a domestic hot water recirculating pump, but at different points in the logiical daisy chain.  If two X10 devices are wired to provide power to the pump -- one ("A") through a timer and the other ("B") bypassing the timer, there's a chance that B could be backfeeding AC to the output of A while A is in the OFF state.  Can X-10 devices tolerate this kind of backfeed, or must I isolate them with a relay?

[Brian H]

For (A). Is the X10 module going to feed the timer or is the timer feeding the X10 Module?

Are you using an X10 Appliance Module to do the (A)&(B) switching?

The X10 Appliance Modules have a ratchet switch in them. To tell if it is On or Off and activate or not activate the ratchet. It has a sensor circuit. It maybe possible that the back fed AC could fool the other module and it will ratchet a few times trying to change its state.