Systemate 2000 calling for heat

I have a Systemate 2000 which doesn't seem to follow the on/off setpoint. Looking on the LED display I have a store temp of 73degC a on setpoint of 65degC and a off setpoint of 68degC. The boiler is still been called for, after about 20 mins the heat call is cancelled and everything stops as per normal.
I guess it's probably the PCB, but wondered if there was anything else I should check?
Many thanks

Tricky possibly this one. It could be the pcb of course easily checked by swapping the pcb for a tested one, if you want to try this let me know and I can work with you to try this without causing bankruptcy! Other thoughts, what temperature are you getting out of the boiler, basically the higher the temperature the better the system works. The boiler should be on Max as recommended by Gledhill, if you can actually measure the temperature (meat thermometer maybe) that is best as what boiler controls saying they are doing is not necessarily fact. Other thoughts sensor issue they are active sensors so have a chip at the end and of course they can fail and tell fibs. I think I would look at pcb swap before swapping sensors. Is the boiler cycling a lot this could indicate a reduced flow from boiler to Gledhill which again would reduce the heat exchange efficiency. Some thought to think about. Regards Murray

Hi Murray, thank you for the reply. I've had another look at things after your suggestions. I have a thermocouple to measure the boiler temps, when I have the issue the boiler output is about 74degC with a return of about 64degC. At this point is when the boiler just shuts off, waits about 90 seconds then fires again. When the boiler is off for the 90 second period I lose a couple of degrees o  the thermal store temp (as the towel rail circuit is the same as the store circuit). Reading the boiler manual, when I have it set to max (which I always do), it should have an output temp of about 82degC. Given that the boiler cuts off at 74degC it's looking more like the boiler end - would you agree?

74 degrees does seem low and with the upper set point at 73 it is a bit close for comfort! Is there a friendly neighbour with a similar boiler that you could compare temperatures? Depending on which boiler you have it may not be a big ticket item to swap. I'm not a heating engineer by the way electronics is my poison but just applying a bit of logic to this (-: