Reliability of Fernox Express Inhibitor Test Strips

[sharpener]

Because the price of the official pots of 50 of these test strips is so high I bought a packet of five for £6-99 from ebay, arrived without instructions or colour matching chart.

 

The online instructions say read the strip within 10 seconds but they showed little colour by then. However a dark brown shade developed after about 30 secs. Google AI says this means they are time-expired or contaminated.

 

The system was power flushed before the HP was fitted in 2024 and Adey inhibitor and biocide added afterwards. I am not particularly concerned but both years since, the Vaillant service technicians have said that they do not test inhibitor strength.

 

Should I be worried? Should I return them to ebay and claim a refund? Are THESE PHP tests at £3 per test any better? Is there an alternative?

 

TIA.