Already suffered from some leakage of our central ...

Already suffered from some leakage of our central heating boiler. At annual maintenance indicated, but they could not find anything. Then again a mechanic who had found the cause within 10 minutes. Rubber ring had to be replaced. Not heard yet 3 weeks later. Called and they had to see if the part was there. Would be called back; however, it did not happen. Called 1.5 weeks later; same story.

Update February 20, 2019:
After 1.5 years and several visits the problem has been solved. We still received an invoice, but after sending the story, we did not have to pay it anymore.
Valuation changed from 1 to 3 stars.