Intermittent hot water problem wb combi

[pete green]

WB combi has recently had it's annual service. It has been working reliably up to that point for many years.
Now we keep losing hot water - temps on boiler increase over 100 on the display and it shuts down heat.
Engineer claims it's coincidental and must be a blocked heat exchanger that has nothing to do with the service.

Is this plausible or is there something else to look for ?

 

[Deleted member 120897]

Sounds like it could be a coincidence. I would check the flow and return valves are open or any other valve that may be shut off, eg a filter.