Howden / Lamona HJA8630 runs all day, makes knocking sound..

sorry of this has been dealt with before, but unsure how to phrase the fault.

Howden/Lamona HJA 8630 integrated dishwasher, approx. 4 & a half years old. In the past 2 weeks it has started doing the following:

1. Sometimes, on rapid, economy, normal and intensive programmes, I will start the dishwasher before going to bed. In the morning, the thing is still making noises and is very very hot inside. Sometimes I set it before I go to work (have stopped doing that now) and when I get home some 10 hours later the thing is again still making noises and again very hot. Occasionally, it runs for a normal length of time, but
seems to do so with cold water not hot.

2. I often use the pre-wash (no heat) before doing a proper cycle. This is supposed to use cold water. This cycle does complete in its allotted 14 minutes, BUT I am now finding that when I open the door it is just as hot as on the high temperature cycles – it literally knocks you back with the heat and steam when you open the door.

3. Often when I start a programme, any programme, it now often spends up to half an hour making a kind of regular dull knocking sound before I start hearing a woosh and the water spraying around inside.

4. All programmes perform fine as far as the expected cleaning / rinsing results are concerned.

5. I use 3 in 1 Finish tabs, but also use salt and rinseaid as it is a hard water area.

6. I haver checked inlet and drain hoses – no kinks. The machine drains fine and filter is clean.

7. The control panel buttons and lights seem fine – I am not getting any of the flashing lights or inability to switch programmes that some other report.

I am obviously worried about running this when I am not there ( or even when asleep ) due to the heat issue.

Any ideas – thermostat ? PCB ? ( I know it’s a Beko and am this close to ordering a new PCB to try… )

Howdens are quoting almost £250 for a 12 month guaranteed repair, and £132 for a 3 month guarantee repair. I would like to fix it myself if possible !