Calor gas heater querie

[psmk2]

I just bought a new calor gas heater for my garage and it works great apart from 2 dark patches on one of the burner plates...any ideas

 

[gasbanni]

Are you doing anything in the garage that causes dust ?

If you've hot an air line when the heaters off blow air at the plaques from the front not too high a pressure gust a gentle dusting down.

 

[psmk2]

Hi.....i tried that with my airline and it did blow some dust out but the same patches appear

 

[gasbanni]

An image will help.
Was the heater in use whilst dust was been produced ?