Found this thermometer which i've glued the thermocouple onto the header tank to give an indication if anything goes amiss. Not sure how useful this is but its a quick and easy job. See link https://www.ebay.co.uk/i/312874927940?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid...

Excellent - the STC 1000 costs £6.51 from Singapore - its a no brainer really!

Also the ultr sonic sensor on the header tank is a great idea.

Brilliant - thats a big saving, out of interest where did you fit the sensor?

I like the look of this .......
https://www.ebay.co.uk/itm/DIGITAL-TEMP ... .l4275.c10

Haydn - quite right this has done the rounds, I see 'graham at work' had a float system that worked for him. Interesting subject matter..... FYI Geof I have a 2.5td.

Thanks Bob.... I was actually thinking of installing a float switch in the filler cap, that way no damage to the header tank and only a new cap if it fails. There are so many types of floats to choose from which may not have been readily available 10/12 years ago, thank you Amazon!

Thanks for the heads up about the baffles etc, I still think a float system may work using a vertical float -- see example: https://www.amazon.co.uk/Liquid-Sensor-0-220V-Stainless-Vertical/dp/B07S7QG3LL?ref_=Oct_RAsinC_Ajax_10256554031_5&pf_rd_r=Z39DF5JX7CEYY11AJNEZ&pf_rd_p=54bbabb3-ccfc-55e...

I was wandering whether a side entry float could be used in the header tank with a buzzer or led connected to indicate a low water situation. Here is a link to what I mean https://www.ebay.co.uk/itm/Stainless-Steel-Liquid-Water-Level-Sensor-Horizontal-Mounting-Float-Switch-30W/401830614794?var=67165...