How do disputes between a primary insurer and an excess insurer get resolved in Ontario?

A primary insurer responds first, up to its policy's limits, while an excess insurer's obligations only begin once the primary policy's limits are actually exhausted - excess coverage sits on top, not alongside, the primary layer. Disputes between the two commonly arise over whether the primary limits have genuinely been exhausted, how a settlement or judgment should be allocated across the layers, and which insurer controls decisions like settlement authority once a claim approaches or crosses into excess territory.

These disputes are generally resolved through the specific policy wording of each layer, since excess policies typically define their own trigger conditions and often require the primary layer to be exhausted through actual payment, not just a nominal finding of liability. If you're the insured caught between competing primary and excess insurers - for example, facing a large judgment while the insurers disagree about which layer actually has to pay a given portion - your practical concern is usually making sure the dispute between insurers doesn't leave you exposed or unpaid in the meantime, which can sometimes require your own coverage action to force a resolution.