Try Absolute Tolerance

Most models converge more reliably with relative tolerances, which is the default on the Tolerance panel in Analysis Setup. However, some models converge much better with absolute tolerance. This most often applies to models which have very small values for flow or pressure, as it is much harder to meet a relative tolerance using small numbers.

If a model will not converge with relative tolerance, you can try changing to absolute tolerance. Even better, try the option to converge on either absolute or relative, which will offer the most flexibility.