TOP TANK EMPTY

I have had some work done on my apartment a few weeks ago and I have just noticed that the top tank is empty.
Should I fill the top tank with water, and what damage do you think has happened as I have been using the hot water while its been empty.

Thanks for your help

Yes fill it up now!!!

Probably no damage will have been caused provided it still gives you hot water. The unit will stop working some while before any damage is caused by low water level.

Don't be surprised if you have to add several buckets of water to bring it up to the correct level...

Cheers, Mike