Chan Abraham handed in his notice and left the company on Wednesday.
The news comes after a turbulent year for the 7,300-home association, which was downgraded to non-compliant G3 for governance by the HCA, in January 2017.
The HCA concluded tenants were at risk of “serious detriment” through a failure to carry out up-to-date gas safety checks.
An internal audit revealed that more than 1,000 homes had not had a valid gas safety certificate for at least some part of the previous two years, they delayed informing the regulator of non compliance.
The Health and Safety Executive is investigating the HA for non compliance with gas safety legislation.