Thanks for responding.
This may be misinterpretation but the system was installed by a company called Gas Flair 2 years ago and it was power flushed. Something else was put into the system to help protect the boiler, can't remember what it was called.
Both DHW and CH thermistors are fine...
Sorry for the essay...
Came to turn the tap on a couple of weeks back and no hot water. Went to the boiler, it was locked out. Pressed the little red button and the boiler fired up ok only to lock out 5 or so seconds later. It keeps doing this, 5 seconds and it locks. It also keeps the...