Abstract—The paper proposes the assessment of regulatory and market frameworks enabling the flexibility provided by a multi-energy system. Flexibility is increasingly a precious resource for system operators to recover electricity network issues due to uncertainties of renewable generation. Multi-energy systems are a reliable source of flexibility and a mean to easily transfer flexibility from coupled energy carriers. To carry on the assessment a real district heating plant operating in the Milan area was adopted. First, flexibility is up/down margins on the short-term plan of the plant to meet the heat demand and bids for day-ahead and intra-day energy markets. Then, flexibility is a set of bids on the dispatching service market. The study considers the plant coupled with the heat network, electricity and gas networks are negligible. A multi-carrier load-flow algorithm supported the feasibility analysis. Assessment of regulation and market frameworks considered five scenarios, the first business as usual and the other ones representing regulation evolutions. The results promote multi-energy systems as reliable source of flexibility that can be greatly increased by relaxing symmetric constraints and dropping some cost components. Index Terms-- Ancillary Services, Flexibility, Markets, Multi-Energy Systems, Optimization