I've inherited a glow worm space saver mk ii boiler in my new house, it makes a noise like trapped air. almost like a kettle boiling every now and then, it isn't a permanent noise.
I've bled all the radiators, twice, but it still makes the noise.
Before i call in the plumber is it...
I have a metal ceramic hob with a metal surround. I'm not sure what the metal is, maybe stainless steel
I recently cleaned the metal surround with 'Cillit Bang power cleaner grime and lime' spray.
I left a particularly bad stain on the metal 'to soak' in the product. I returned some hours...