Top advice Tony.
Its working now! I think your air lock diagnosis was spot on.
Solution:
Last night I took off the rad nearest the boiler, flushed the rad (no actual 'sludge', more the consistency of ink), also drained a tiny bit of water (it was very clean)out of the system via the In rad valve.
Then replaced the rad, fully opened all rads, turned the old faithful baxi bermuda 551 back on at medium temp, balanced all the rads in the property. Hey presto.
Don't know whether it was air (would make sense as the DHW inlet into the hot water tank is the 2nd highest point after the filler tank). But the system seems to be circulating well now.
Cheers,
PS, Have another one;
Since all this activity, the analogue timer switch (very simple, with 2 time slots on a 24hr revolving dial on the front, plus a Timer/Off/Constant toggle switch on the side) has given up the ghost. What would be a fair price for fitting a new one ?
BigDave47
January 2009