The same thing happened to my BG 437. It tumbled but gas stayed on for 10-15 seconds each time on the cycle with no heat being produced. I tested the thermostats - all working and then replaced the FFD (flame failure device) this is an electrode situated in the path of the gas flame. Has worked perfectly after this. It is held in by one screw and got at by removing both small panels at the back of the machine
john kirk
January 2008