On-Call Welcome yet again to On-Call, The Register's weekly column in which we take readers' tales of odd jobs in odd places, tart them up and present them to you as a bit of light relief on a Friday.

This week, meet “Gary”, who once had a trouble ticket land on his desk stating that “the PC would reset every time the customer flushed their toilet.”

Gary's first thought was that this was “probably static from the customer walking across their carpeted floor, touching the keyboard before sitting down, static discharge doing the rest.”

But then he read more closely and realised the PC was on a farm. Once he visited that farm he found that “the floors were all hard-wood, so that shot that idea to hell.”

The user then suggested Gary observe the PC as they walked to the bathroom. Gary heard the unmistakable gurgling that resulted and watched as the PC did indeed reset itself about two seconds later.

Which was so odd that Gary asked the user to flush again. This time he thought the spotted the “a slight dimming of the lights lasting all of about half a second.” Cue a series of questions about fuses, circuit breakers, power load on the circuit. To which the users answered that they'd had a brand new circuit wired for the computer, but hadn't purchased a UPS for it as they felt it shouldn't have been necessary.

“After some thinking, I asked about where their water came from,” Gary tells us, “and that's when they looked at me kind of funny and replied 'from a well across the drive by the barn'.”

At which point Gary asked when the pump had been replaced, a question the customer could not answer with any more precision that somewhere between one and two decades in the past.

Gary now developed a hypothesis he described as follows: “When the toilet was flushed, the pump had to kick in to fill the tank and that when the motor kicked in, it had such a current draw because the brushes were probably worn out.” That current draw was what dimmed the lights and therefore disrupted power supply just enough to also trip the computer.

The customer was willing to entertain that theory, found a friend willing to replace the pump and found doing so fixed the problem. And just to flush the problem completely, they bought a wee UPS too.

What's the cleverest correct diagnosis you've ever come up with? Write to share your story and you could be next week's anonymised On-Call hero. ®