Thanks for your reply. I have downloaded the information for the DOMIcompact F24B, as you suggest - section 4.6 of the manual. However, my time clock does not look like the one described there.
To the left of the 24 hour clock on my timer there is an "eco comfort" button (top) and "reset" button (below). Above the 24 hour clock there is what looks like L in a circle, then M, then a small arrow (reading left to right). Below the 24 hour clock there is a minus sign, then a P, then a plus sign (again, reading left to right). The boiler was installed about a year ago.
Does this help?