Maybe there's "new" air in the system because you emptied it out after bleeding the radiators? Try bleeding then topping up after you bleed rather than empting first. Also check all the bleed valves are totally closed on the radiators, and also check near the hot water tank for a bleed valve (probably in loft or cupboard) We had a similar issue on another make of boiler where pressure would drop over time (a few days) but gradually with tightening things up and topping up the pressure from the tap at the boiler, it seems to have cleared. I think our system was suffering from not having been used constantly. If your system is off for periods of time, try running it more regularly? Otherwise it sounds like a leak/burst somewhere.
Drew
February 2009
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