Mike,i dont know what you mean, I have sorted the air block in the HW side of the CH problem solved. The only problem I am left with is the back boiler in the fireplace which has nothing to do with the CH has an air block, then I have to replace the immersion heater as it has now blown,god I love to be busy,not.
You would be a little confused if you had spent 3 days trying to solve this problem thanks anyway Ian