storage heaters?

I have adopted technoheat storage rads and tried to find instructions on the web...

There are 3 knobs on the side of the gray casing 1 charge, 2 comfort and 3 output, The first seems to be highest on the middle settings and confort makes a click like a thermostat half way up range, the outpt seems to make little difference, where ever set, setting it to charge is guesswork

Anyone tell me how tp work these or find a manaual to tell me