Yes im competent, and gas safe, by-passed to confirm my suspicions about the defective sensor, remeha technical man was pants. Told me the sensor can't be replaced and that the whole gas to water heat exchanger had to be replaced, £500.00 no thanks.
You are not reacting in the responsible manner expected of an RGI.
Furthermore, we dont see you posting in the CC part of the site for RGIs.
So what is your G-S number then?