Faulty boiler thermostat?

[Connor Williams]

Hello guys, working on a faulty sabre he boiler and the burner for the hot water only stays on if the temperature gauge is turned up full, if you try and turn the temperature down the burner switches off and on resulting in temperature fluctuation.
The boiler has a seperate hot water heat exchanger, could it be a faulty thermostat?
Many thanks for any suggestions,
Connor

 

[stevetheplumber]

Hello guys, working on a faulty sabre he boiler and the burner for the hot water only stays on if the temperature gauge is turned up full, if you try and turn the temperature down the burner switches off and on resulting in temperature fluctuation.
The boiler has a seperate hot water heat exchanger, could it be a faulty thermostat?
Many thanks for any suggestions,
Connor

heat exchanger blocked so will only run on high anylower and it cuts of due to heat build up