Posted By Roger the Dodger You will need to read up on the Pressure Systems Safety Regulations. A summary is available via the HSE website and the free publications/leaflets section. I no longer have much to do with this side of safety work. I would doubt is the PSSR regs are particularly prescriptive about specific safety valves/componets in any particular steam system. I think the general principle is that the examination/test period for any particular depends upon the opinion of your pressure systems surveyor (typically from an insurance company). Who ever your competent person is will draw up a 'written scheme of examination' specifying inspection, test and maintenance requirements etc. This is usually via a Chartered Engineer. I suggest you speak to your insurance company.