strange pir security light issue

Good evening all...

Got a strange one here. Customer had a standalone pir feeding a sec light that 'stopped working'.
when i got there, he stated that the light would come on and not go off. Had a look and found no problems with the connections so went through a basic setup procedure using the sensor set up routine common to most. Hey presto, seemed to be working just fine. came on, went off after set time and so on. left him happy....?
Called later that night, light came on and wouldn't go off! arranged to go back and swap sensors for a new one. Did this and got it working just fine...again. No charge this time customer service etc. Later that night he called again. light won't go off!? Soooooo, went back (again) tonight just as dusk falls and spent 2 hours out in a cold garden with this bloomin light that i cannot for the life of me get to reproduce the same problem. comes on. goes off. several time and sensitivity alterations later, it still does what it should be doing. The customer comes to check for himself and sees the exact same thing. Got a call about 15 mins ago.....
there is no heat source near the sensor, nor other lights etc and he is adamant that nothing has moved in the garden.
Any other ideas would be very welcome as i am out of them myself.

Regards.

This does not help you at the moment, but if you get to the stage where you go back and the light will not extinguish, cover the fresnel lens with black tape and see what happens then.

Intermittent power failurs are setting the PIR to 'manual override' mode

are you sure he isn't switching it on and off?

The steam from my boiler flue sets mine off. Could it be that? Or maybe a Ghost cat or something?

If not, set the dawn/dusk setting darker and the sensitivity setting to less sensitive so effectively it has to be pitch black and the intruder has to be standing in front of the light waving his arms about

Like A1Electrical's customer, I had a standalone PIR feeding a separate light that 'stopped working' in that the light would come on and not go off. This happened on Monday evening; at first I put it down to a short power failure that we had on Monday morning having set it to manual over-ride. Having switched it off for up to half an hour, I assumed that the unit had failed, and started looking for a replacement PIR.

The purpose of my post is to comment on the different qualities of the offerings from Toolstation http://www.toolstation.com/shop/Lighting/Exterior+Lighting/180+External+PIR+white/d220/sd2663/p19615 and Screwfix http://www.screwfix.com/prods/11291/Lighting-Lamps/Floodlights/PIRs-Photocells/Stand-Alone-PIR-140 - in the hope that it might save someone else's time & effort

I went first to Toolstation - my excuse is that it's nearer, and I've had reasonable (non-electrical) stuff from them before. I should have realised my mistake from the instructions, which start "The prodrct is energy-saving automatic switch adopted integrated circuit and be precise detecting components, IT can be on when body detect it and be off automatically after body leave, its performance is stable." (n.b. this is an exact quote from the leaflet.)
The design, quality and material strength were awful - I gave up when a fixing tab snapped off, but should have done so earlier on finding a 3-gang terminal block (i.e. no earth.)

The Screwfix item is under a quid more - but what a difference, from instructions to design to material strength. It's obviously too soon to tell how long it will last, but at least it has the feel of being reasonably good. You can see the instructions .pdf file (and user comments) from the web page.

Usual disclaimer - no connection with any company, just a customer.