I have a Worcester bocsh 35 CDI II. Last year the hot was cycling and after advice from here I replaced the secondary heat exchanger and all was well. Now it's doing it again. I have had the exchanger off again and connected a hose to it and run water through it. The water ran through well and not a lot of crud came out. Refitted it and it hasn't made any real difference. How blocked do they have to be to cause the cycling? When i ran the water through it, it didnt seem blocked at all. Could something else be causing it? The heating seems fine. While the hot tap is on the DHW demand light stays on but the flame turns off.
Thanks
Adam
Thanks
Adam