worcester boiler 28i junior eco button keeps coming on

I can't find an answer to this, apologies if it's already been covered.
My 10 year old worcester boiler 28i junior eco button keeps setting itself to on and I've no ideas why.
Also, the hot water from the taps is very hit and miss. I.e. Runs hot then warm then cold, there is no pattern to this that I can see. Just that is does seem to be better with the eco button off, but still not ideal.
The heating via the radiators is fine though.
This has been happening for some time and I've had the heat exchanger replaced and I have a magnetic filter installed.
I am waiting to get the thermister(?) replaced, it's on order, in the hope that this will fix the problem.
Should I also get the control flow valve replaced as well?