Intermittent non-starting fault in 2013 van

Soot2006

I bought a Peugeot Boxer (2013; 77,000 miles) about 6 months ago.With the Covid situation I didn't do much with it for quite a long time so have only covered about 1,000 miles since purchase, mostly in the last 2 months.

In the last few weeks it has started intermittently not starting, giving a "excessive radiator temperature" error on the dash. So far, it's always started after a few tries. It seems to do this mostly after the first short run of the day, but seems to be becoming more frequent (although, so far, only once a day despite several restarts during the day). My mechanic had it for a day and there was no error code logged on computer. He started it upwards of 50 times and never had a problem. Checked temp sensor in various ways and couldn't fault it. The next morning = same fault.  Mechanic says we can change all the sensors one by one, but with an intermittent fault that could get expensive until we happen across the correct one.  Not very MSE!

Just thought I would see if anyone had encountered something like this or if you had any advice to save some pennies before we start replacing things that may or may not be broken.