Second hand equipment warranty

I bought a second hand commercial dishwasher April 2017. It came with a 6 month warranty from the supplier. An engineer has revisited on several occasions to fix similar issues since first purchased. I have call-out texts which I sent in 2017: July x 2 call outs, September, October & January 2018.There was one occasion where the fault was down to us causing a block in the drain in October & this call out was paid for, but others were machine electronic failures.
So at this stage I'm fed up of the issues & have been waiting since mid January for the latest issue to be resolved (4 texts & still no engineer despite replies acknowleding faults!)
I've suggested to the company I purchased it from that the machine has been trouble since day one & should be replaced but they claim too much time has passed.
Do I have any legal angle to impress on them or recourse with regard to getting it replaced or a full/partial refund on the purchase price?

Thanks, T.