I had a problem with the pilot light not staying on. The pilot would light but as soon as you release the pilot button it would go out. Mine is a Brivis Buffalo 85 central heating unit. Following everyones advice (thanks!), I went and bought a thermocouple and my heater now works. I got a Brivis Thermocouple (part B009065) from Totaline, Roden St in West Melbourne. I could have got a Honeywell equivalent from Reece but I decided to get the Brivis branded one. I probably got touched in the process at $50. I installed it myself by removing the whole pilot assemby which involved the capillary tube fitting and pilot gas pipe fitting and one screw on the pilot assembly. I then yanked out the thermocouple with a pair of pliers then pushed in the new thermocoupling by hand. I then loosely refitted the pilot unit, the pilot gas pipe and the new capillary tube taking care to not cross threads which is dead easy to do. Then tightened everything and tested for leaks with soapy water. Then started it up and it worked just like a bought one!