The ornamental design for a header for solarcollector, as shown and described.
FIG. 1 is a right front perspective view of a header for solar collector, showing my new design;
FIG. 2 is a rear elevational view, thereof;
FIG. 3 is a top plan view, thereof;
FIG. 4 is an end view thereof;
FIG. 5 is a front elevational view, thereof;
FIG. 6 is a bottom plan view, thereof; and,
FIG. 7 is a perspective view taken to a reduced scale, the broken-line representation of the assembly comprising the five additional headers and the solar collector mats being included solely for illustrative purposes, forming no part of the claimed design.