Vokera maxim 24e hot water probs

[Plucky]

Going to look atvthe above boiler for a mate. Not getting decent hot water, boiler fires when tap opened but temp dial on boiler ever exceeds 20 degrees. Boiler runs the whole time.

Any ideas? Maybe thermistor or something?

 

[Billy Bob Bob]

check thermistor,gas pressures,plate heat exchanger