You've not stated exactly where you purchased the pump (i.e directly from the manufacturer or from another supplier?) or how long 'a few months' actually is.
If you bought the pump from a supplier, other than the manufacturer, your rights are with that supplier not with the manufacturer. So, if you purchased the pump from, say, a plumbing supply company you should contact them, not the manufacturer.
If the pump failed within 6 months of purchase, there is a legal assumption (unless there is evidence to the contrary, such as incorrect installation) that the problem is due to an 'inherent fault' (i.e. poor quality components or poor manufacturing). You can insist that the supplier provides a repair or replacement. (You can indicate which of these two options you prefer but the supplier can reject that option on the grounds of economic viability).
Beyond 6 months (and up to 6 years) from the date of purchase, you retain the same rights to receive a repair or replacement, from the supplier, for a problem caused by an inherent fault. However, it would be up to you to show, based upon the balance of probabilities, that an inherent fault was the most likely cause of the problem. (i.e. there is no longer a legal assumption that a product failure is due to an inherent fault).
So, if you bought the pump from somewhere like a plumbers' merchant, you should return the pump to them and insist that they remedy the problem. (They would probably choose to replace it and then seek compensation from the manufacturer).
All of the foregoing text relates to your statutory rights. A warranty is a 'gift' from a manufacturer and is entirely separate to your legal rights. As such, each manufacturer has the discretion to determine any conditions which apply to the warranty, which might include provision of credit card details.
If possible, you should claim under your statutory rights and