No, you can never withold rent without a court order. If the landlord did not fix it within a reasonable amount of time (7 days is definitely reasonable), then you would have called the local health department to do an inspection and have the rental unit declared uninhabitable, since heating is required to make the unit habitable (legal to live in).
At this point, you would have gone to court to have rent prorated for the amount of time the house was uninhabitable. Since things never escalated this far, you have no recourse. Be glad your landlord actually fixed it, and within a reasonable time frame.