ravenheat rsf84et boiler fault

Hi if anyone could help me with this I'd be extremely grateful.
The boiler mentioned has started to have a mind of its own.
On either setting hot water or water/heating the boiler fires up on its own and stays on, I know ravenheat is regarded as **** but I cannot afford to replace it and so am hoping it's a particular sensor that I should replace first- thanks steve

 

Hello and thanks-what other info would be more likely to be of help -thanks steve

 

Hi peter- yes they do- any help much appreciated thanks Steve