Replacing 'Sunline' immersion thermostat

[dmilbank]

I have recently decided to rely on our immersion heater during the summer for hot water, considering it to be cheaper than using central heating system. I soon realised that the thermostat was not working! Is it a simple job to replace? The thermostat is probably 25 years old and made by 'Sunline' Type SO-A-S, which I have failed to locate on-line. Can anyone advise if job is as simple as I imagine & suggest alternative make.

 

[picasso]

as electricty is about three times the cost of gas cant see how it can be cheaper to heat your water with an immersion heater, get it fixed as an emergency back up but use your boiler to heat the hot water.