Coolant problem / power loss / limp mode

[DCB]

My March 2017 170ps engined Motorhome (so the chassis will be late 2016) has developed this problem. Drives normally from cold then after maybe five miles the engine goes into limp mode and the temperature gauge shoots up to the top from just below the middle and I get an advisory to pull over when safe to do so on the dash display. Fault disappears when parked for a few minutes then comes back shortly after setting off again. Could be the thermostat not opening, I guess? The MH is parked for long periods between runs, to save the Injectors...

[Coxyx11]

Driving on a motorway in southern Italy our 2018 170bhp Tourneo (62000 miles) went into limo mode but with NO indication at all on the dash.
A coolant leak was obvious from drivers side & expansion tank cap so recovered to the nearest garage.
Water pump had failed so new item fitted.
Van tested but went into limp mode again when up to temperature.
Local mechanic was ademant the head gasket had failed & was pressurising the system.
Checked the forum & spotted these entries so asked them to change the thermostat & housing first.
Spare fitted was not like for like but I was informed (by the Italian mechanic who spoke no English) it was an updated item with one main difference only 1 sensor instead of the original 2
Van tested & no more limp mode, imagine the mechanics face plus no fault showing on the dash despite only 1 sensor connected.
Phoned Ford Doncaster service & they confirmed the updated unit & there will not be an issue with 1 sensor not in circuit.
Old unit opened up & found heavy scaling within