Vauxhall Combo heater stopped working in van and temperature gauge gone real high

Check coolant level first . Dependent on results , simple causes , jammed thermostat . Bigger problems cyl head / gasket .

OK thankyou , if coolant is low , can you put just water in or different

If coolant low or empty , you are better topping up with water till finding out cause of loss .Coolant is dearer to buy than water which is free . Coolant will need replacing once you locate and repair fault anyway . Depends on findings after checking what your next step will be ,hope it's something minor like a hose and you stopped in time before causing any big damage

Coolent is empty ,

You have to fill it and then run the engine and look for any leaks , especially from any heater hoses if any at rear of engine . Watch coolant reservoir as it warms up in case it is
filling up / pressurising and radiator hoses get hard also due to pressure .

Thankyou for you help, very kind of you and helpful. Dont quite understand last bit , about filling up reservoir and having to watch it . Could you explain another way please

If your cyl head or gasket is leaking it can show in header tank / reservoir by filling up with coolant and over flowing due to excessive pressure pushing coolant . You could also remove thermostat and check if stuck closed .

OK thanks, think i got , although no mechanic. Will top up with water in morning . Run the engine and see what happens.