Does the dishwasher seem to get hot during the wash cycle?
Does it seem to using the rinse aid up?
If its heating then thats what the fault will be is the rinsing side of the dishwasher. As this is when it uses the rinse aid and does the water softner as well.
First though what you can try is remove the spray arms and give them a good clean. Make sure all the holes in the arms are clear.
If they are fine then its possibley a fault on the regeration unit underneath as this is what does the softing of the water and should stop this from happening.
To check this if you are looking at fixing it yourself you need to access the salt chamber underneath the dishwasher and in there is the regeration valve. You need to test this with a multi meter and see if faulty. If so then you need to replace this and hopefully that will cure the fault and will then sort this fault from there.
As if its heating and you are using rinse aid, salt and run clearners through it then its usually the water softner regeration valve at the bottom at fault not cleaning the water during the rinse cycle and this is what causes the fault you have here.
If the dishwasher is heating when it shouldnt then it will be the control board. Thats the only thing that will cause this fault as its the control board that brings the heater on.
Now as to weather its worth fixing this depends on how old it is. As i dont know the model so if its quite a few years old then its probberly worth replacing the dishwasher as the control board is an expensive part.
But Hotpoint do a fixed price repair for £110 all in so no matter what parts it needs you only pay £110.
But given the cost of £110 it may well be better putting the money towards a new one.
I know its not good news but if you could remember to rate the answer that would be great.