|Random image of a projector - not the one you have ;-)|
...If the message is appearing on your computer screen then it is just a suggestion. If a teacher is getting a message on the [Promethean] board itself from the projector then you may need to clean the filter. I personally clean ours here but some people turn in a work order. All you need to do is find the filter on the side of the projector and pop it out.
There is a little piece of foam usually that simply needs to be vacuumed. I bought a small vacuum that I keep in my office and the teachers will just send it down with a child and you can clean it in about 15 seconds. I just vacuum around the foam or insert and the plastic piece itself to get the dust off. When the teacher puts it back in there is a reset option on the menu that they need to reset to oh it looks like oh but it really says 0 hours.
Be careful when you vacuum the foam…hold on to it tight. We had one from an old projector that was fragile and I accidently got it sucked into the vacuum. Before I bought one for my office I used to get the vacuum from the custodians closet across the hall and use the wand to clean them. It is easy and saves the teacher a lot of time and hassle. If you do not clean the filter then eventually it will overheat and won’t turn on. If a projector wont’ come on this is the first thing to check. Then of course check the bulb.