No reply after several weeks and a couple of prompts so I have given up and started looking to buy a new one - but definitely from a different manufacturer as this one is obviously unreliable. I have tried my slow cooker but I still prefer the convenience of a pressure cooker.
I first looked on John Lewis's website but they only have two stovetop cookers and neither of them suitable. I don't want an electric one as I need something that can be used in the event of a power failure - something we occasionally experience during winter storms.
Browsing the magic of the internet I came across the Lakeland website - I had completely forgotten about them. I used to buy their products many years ago and was always pleased with them.
Ten minutes later and one of their stainless steel pressure cookers is ordered and hopefully on its way to me soon - provided Hermes doesn't lose it.