This is improper for the HOA to refuse the repair. The repair was needed to fix a common utility. As a result, any associated repairs that are done in private units are the problem of the HOA and as a result, you should indicate in writing that the HOA is responsible for the costs and then, you should inform the agency who handles HOAs and HOA complaints. This is usually the attorney general (if the HOA is a non profit as it should be) or the county or town prosecutor. Make sure you keep records of costs (including at least three estimates) to use to show what has occurred. Take lots of photos (near and far), label everything and try to get affidavits of the individuals who did the repair.