The larger tank is your cold water storage. (CWSC) The small will be for your central heating.

Have you checked that the gate valves are fully open (usually in th airing cupboard)? Is there water in the large tank - levels ok in here? The float valve working right?

If you still feel all is well then you have a few options to see if it really is an airlock......

close off the isolation valve to the CWSC and drain down with taps open then refill.

or

turn on cold tap place finger over spout for a short while and see if this shifts the lock - sometimes you can blow down the tap to move the aor depending on how your lungs are and where the lock is.

or

get a short length of hose find feed for cold water in CWSC and blow - don't fall in! Ensure taps are open...

thanks, i'll have a look in the loft tuesday which is my next day off work and report back

with folded rubber glove for good seal , covered tap outlet with palm of hand . held in place for about a minute. lots of noises coming from pipes and tank in loft. I now have cold water back in bathroom cold taps and toilet. air drained out of bath tap. thank you for your help