Unfortunately your pet insurance policy will not pay for all your vet fees. Policies do vary but you generally find that you have to pay veterinary fees for pre-existing conditions, routine and preventative treatments, elective or cosmetic treatments, and any treatments which are considered non-essential or excessive.
Unfortunately there are very few policies which will cover pre-existing conditions.
The definition of pre-existing conditions varies a little from policy to policy but generally they are those conditions that your pet had before the policy came into effect (including those which started during the waiting period).
You will also usually find that the definition is expanded to include any condition which is connected or related to an accident, injury or illness you knew about before you took out the policy.
Connected or related conditions are a highly contentious area as pet insurance companies have been known to claim conditions are related when many vets would disagree.
(The Financial Ombudsman receives many complaints each year about pet insurance rejecting claims on the grounds that the condition is related to a pre-existing condition).
Routine and preventative treatments
You pet insurance policy will not normally pay routine health checks or preventative treatments such as vaccinations, flea and worming treatments, nail-clipping, bathing or de-matting.
They will also not pay for routine spaying or castration.
The majority of policies will also not pay for preventative treatment such as spaying to prevent false pregnancies or mammary tumours (but some will so it is worth checking).
Most policies specify that your pet must have all routine and preventative treatments recommended by your vet (at your expense).
Most policies will not cover any treatment fees which are related to mating, pregnancy or whelping. There are a few policies which cover breeding as an optional extra.
Cosmetic or elective treatments
Pet insurance policies will also usually have an exclusion to cover elective or cosmetic treatments (such as cosmetic surgery or removal of dew claws which are not infected or damaged).
Many policies will also exclude investigative tests that you choose to have but which are not undertaken to diagnose a specific condition.
Non essential treatment
Most policies have a clause which states that they will only pay for treatment that they consider to be essential and not excessive.
This is another controversial area as clearly this is often a matter of opinion which is why most policies reserve themselves the right to get a second opinion from a vet of their choice.