If the pipe came with the machine and the machine is under gurantee then the pipe must by definition be covered by the guarantee - they can't exclude a specific part from the overall terms of the guarantee.
Their claim that the pipe may have been damaged by a rodent is pure guesswork on their part and they have no evidence to substantiate it.
Their responses have no logic - on one hand they say the pipe is not ccovered and on the other hand they claim it's rodent damage - if it's not covered then it's not covered - they don't have to introduce rodents to disqualify your claim - but they do strangely?
The pipe may indeed have been damaged by a rodent but until they inspect it they are not in a position to form an opinion.
The warranty is owned by the vendor - the people you gave your money to - if in the UK, contact your local trading standards department or call consumer direct who will advise you.
http://www.consumerdirect.gov.uk/
You probably have a claim agsinst the vendor and my eventually get a new pipe - however it may take months to get resolution and cost you the price of several new pipes - it may be best to just shrug and send for a new pipe at your own expense.
Complain clamly if you complain at all.
Good luck...
Peccavi
November 2009