refund faulty goods

Hi, I have been installing alarms for about 8 years and very rarely I have any problems with false alarms. and when I did i was able to solve it. Recently I have installed wired Pyronix Euro46 App alarm but once a while gets false alarms on diffrent sensors. So I did decreased sesitivity...

My husband installed an identical electric shower. He has done hundreds of them in the USA. The shower came but had no hose in so we used the hose from the old one as it was identical my husband had no need for the instructions as they were not in the box too. It worked beautifully for 3 months...