Domestic hot water now works ok, but when i turn the CH on it runs for about 15 seconds then the boiler shuts down and i have to press the reset button to start it up again?
Are the isolating valves under the boiler both really open ( not just plastic knobs pointint somewhere ) ?
Sounds like no or severely restricted flow. That could be caused by a jammed diverter valve although thats uncommon to be stuck towards the DHW direction. Check the pin is fully retracting reliably.
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