Great Hot Water pressure - cold dribbling

[Esskay]

Hi,

Have a baxi megaflow tank with economy 7 heating....when the booster stopped working the thermostat was changed as it had clogged up and ....since then the hot water pressure is still fine and now we have plenty of it but the cold now trickles out..is it just a big airlock in the system or can anyone else suggest somethin? We have mixer taps in the the bathroom and kitchen if that's any help.

Thanks