No fault codes and many thanks for the advice. Am I correct in thinking the TF1 could be the problem rather than the boiler.
If I do drain and clean etc, can I add Fernox to the filter or is that best left to an engineer.
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UPDATE: Just took a look at the TF1 and found some sludge around the magnet sleeve as you would expect but not as bad as some of the videos Iv seen on YouTube. I tried to flush by turning on the bottom valve but no water pressure at all. I checked the bar meter on the boiler and it is 0 so all the water has drained. I tried to refill but no water pressure anywhere. It now has an error code E19. Also no hot water form the taps which there was earlier this morning before I messed with it. Looks like Ill have to wait for CH engineer after all.
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OK so here is what I found. I gave the filter another clean and this time fitted a new main seal ring to the lid which came with the original installation pack. I coated with Vaseline as I don't have silicone. I opened the top and bottom TF1 inlet valves, (which is why I could not repressurise before) and the boiler filled as normal. The leak on the lower valve is as bad as ever and is why the boiler visibly looses pressure. No pressure at all means no hot water either. Unfortunately I do not have a large enough spanner to tighten the valve and see if that fixes the problem. If the boiler senses a leak and slow drop in pressure would that stop the CH from working.
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Also, the boiler will light for a few seconds but then shuts down.