MY HOUSE IS 17 YEARS OLD AND I WANT A MULTI FUEL STOVE,ON CHECKING MY CHIMNEY I FOUND THERE IS A POT LINER DO I STILL NEED A FLEXI FLU LINER AS WELL

Its unlikely you would need a liner after 17 years ,just get it smoke tested, what you will need is a pot liner adaptor(sump adaptor) this seals the stove pipe to the clay pots. Cheers E M Flues

Your original liner may be okay, but I would advise fitting a twin wall stainless steel flexi liner to be on the safe side. All these works come under building regs now, which if you are doing the works, you pay a fee and have the work inspected and signed of. I would advise to use a Hetas registered installer, he will fit every thing to building regs and issue you with the relevant certificate.

Although there are adaptors to fit to the bottom of pot or clay liners these are time consuming to fit and we feel it that in are professional opinion it is much better to have a flexible liner fitted.