my hot water is going cold for a minute then back to hot, I have a Worcester Greenstar 24i junior condensing boiler is around 8 year old also the water comes out of the hot taps very slow any suggestions please
It sounds like a 'cycling' exchanger, which basically means that it cannot shift the heat fast enough so it 'overheats' and shuts off for a bit before cooling and then coming back on. If your hot tap flow had remained good, then I'd suspect a blocked 'system' side of this exchanger, most likely caused by a build up of system sludge. However, since you say the water flow has reduced, then perhaps it's due to a blocked inlet filter which is restricting the flow to the boiler so much that the exchanger cannot shift the heat? Check out the instructions and see if you can track down where the inlet filter is - it should be accessible under the boiler I'd have thought. Check that first. See the wetness you are experiencing? That's 'cos you didn't turn off the mains supply first.
Classic scaled up heat exchanger symptoms,time for a new one. I don't know whether it's a heat exchanger 10 plate or 14 plate though.. https://www.plumbarena.co.uk/product/worcester-87161066850-heat-exchanger-16-plate/#.W1jRRrgnYaE https://www.plumbarena.co.uk/product/worcester-87161066860-heat-exchanger-12-plate/#.W1jRYrgnYaE