12012909 Genuine Medium Burner Diffuser for Bosch, Siemens, Neff Gas Cooktops, BSH Flame Spreader Burner Crown Replacement

Genuine BSH diffuser 12012909 is the medium size, the slotted ring that sits under the cap on a gas cooktop burner. Some people call it the flame spreader or burner crown. It suits Bosch, Siemens and Neff gas cooktops that list this number. Our record doesn't name the burner position, so match it to your cooktop by size and by the number on your parts list before ordering.

How a burner diffuser shapes the gas flame

Gas leaves the injector, mixes with air and rises into the diffuser, which splits the flow through a ring of ports or slots so the flame forms evenly around the burner. Over the years diffusers distort with heat, corrode from boil-overs and get ports blocked with burnt food. Typical signs are gaps in the flame ring, flames tall on one side and short on the other, yellow tips, noisy burning, or slow lighting because gas isn't reaching the spark electrode properly. Cleaning sometimes helps, but a warped or corroded diffuser should be replaced.

Part details

• Genuine BSH part 12012909
• Medium size burner diffuser
• Also called a flame spreader or burner crown
• Sits under the burner cap

Swapping the diffuser

With the burners off and cold, lift off the pan support, cap and old diffuser. Note how the diffuser locates over the burner base and around the spark electrode, as most only fit one way. Set the new one in the same position, refit the cap and light the burner. The flame should form a full, steady blue ring. The gas valve, injector and pipework must be left to a licensed gas fitter.

Questions about this part

Do I need a new cap as well?

Not unless the cap is damaged too. The diffuser and cap are separate parts. If your cap is chipped, warped or rusty, it makes sense to replace both together so the burner seals properly and lights cleanly.