An early warning system, designed to alert people in Carlisle of impending floodwaters failed during tests.
Floods last January affected more than 2,000 homes and businesses
The £300,000 system came after devastating floods struck the city in January 2005, claiming three lives and leaving thousands homeless.
Saturday's exercise was assessing how quickly residents could install door guards and air brick covers.
But some of the 80 homes involved in the exercise failed to get an automated alert telephone call.
Homes in the Crosby-on-Eden area of the city were targeted in the test.
'Sort out glitches'
Staff from the Environment Agency, who were monitoring the exercise, say equipment will now have to be double checked.
Carlisle City Council housing officer Andrew Dixon said: "We have already been in contact with the Environment Agency who helped set up the system.
"Thankfully this was just a test exercise rather than the real thing and we can sort these glitches now."
Last January three people died in the floods, which devastated parts of the city.
The cost of repairing damage to thousands of homes and businesses was estimated at £250m.