Installing 2 x 19kg propane cylinders with manual changeover to supply domestic gas hob. Builder has done the copper pipework but he isnt gas safe so his 'tame' GasSafe sub is planned to do the remainder. I am supplying materials I have bought an MC regulator with PRV and OPSO (which BES say is compliant) but this subby says an UPSO is needed. I have checked regs and also contacted Gas Safe Technical and the manufacturers (Clesse) and they all assure me it isnt required, but this guy apparently wont move - he wont install it without an UPSO. I accept that he may have a personal reason for that, even if it isnt a regulation, but as I am not dealing directly with him I cannot ask! My builder would seem reluctant to upset this guy with whom he has built a long working relationship. Why would I want an UPSO on a 2 x 19kg installation? Surely the point of the flame detect on the hob is that when pressure falls and flame goes out the gas is cut off. There are no credible scenarios other than exhaustion for the pressure to drop on p[ropane supplying just a hob. If it was a CH boiler that might be different! Although I prefer manual changeover if I'd fitted an ACD how would it detect when to change cylinders if an UPSO was fitted? Finally if I need to find my own contractor, will anyone do the job if they dont know the 'history' of the pre-laid pipework?