It looks to be a water inlet issue. Possibly the valve that lets water in has an issue.
From this manual:
http://docs.hotpoint.eu/_doc/F082914_LTF8B019UK_MANUAL.pdf
On Page 16:
The dishwasher does not take any
water in - Tap shut-off alarm
(beeps are heard and H appears for
some minutes on the display)
(the ON/OFF indicator light flashes and
number 6 appears on the display).
Causes:
There is no water in the mains supply.
• The water inlet hose is bent (see Installation).
• Turn on the tap and the appliance will start after a few minutes.
•The appliance lock has been activated because no action was taken when the beeps sounded. Switch off the machine using the ON/OFF button, turn on the tap and switch the machine back on after a few seconds by pressing the same button. Re-program the appliance and restart the wash cycle.
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I also found a post supporting this diagnosis
https://www.northlondonappliancerep...with-error-code-h-on-hotpoint-dishwasher.html
"I have (had) the same problem. Fortunately I have hotpoint cover so called an engineer. He had never seen this code but took advice and decided it stood for H2O (water). He replaced a unit on the left hand side which has an impeller with a magnet in it and a little glass tube with 2 bits of metal. The magnet should open and close these 2 bits of metal indicating water flow."
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Another site suggested that it could be connected with the thermostat and/or heater element. But the above course of action is what I would look at first.