Hi I recently drained my water tank to change some kitchen taps. When I reopened all the stop valves I found I have hot water running fine but cold only from kitchen and sink in bathroom and non from bath. A friend thinks I my have an air lock somewhere is this the case or something else thanks for help in advance.

Good morning Redley,

" a friend thinks i my have an air lock somewhere is this the case or something else"

It's more likely that you have disturbed the mineral build up in the bottom of the tank and some has got sucked into your hot water system. Since there is constant pressure from the water heater a air lock is impossible.
You must shut the water off to the faucets affected and open t6hem up and clean the crud out of them. Before you reassemble them turn the water back on for a minute to flush the supplies. Since all this happened because you don't flush your heater on a regular maintenance schedule let me show you how.
If you do not flush,(not drain) your heater on a regular basis it will build up mineral on the bottom of the tank. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) and some white grains,(lime or calcium carbonate). The whole thing shouldn't take more then a few minutes. Don't forget to flush it out every month. Your heater will thank you for it. You might want to consider cleaning the screens on your areators if you have a high mineral buildup. If thev problem still persists after you have flushed, you will have to drain the heater, remove the boiler drain and go up in the bottom of the tank with a wood or plastic rod, (not metal) and try to break up the mineral and flush it out. Good luck, Tom

Thanks for taking time to help , but I'm not sure which tank to flush, the system I have is a boiler on kitchen wall then an insulated tank in a cupboard in bathroom and also more tanks in loft.I have loosened the pipes off from under the tap what dose not work and there is water there but no pressure pushing it through. Sorry for being so dumb :(

There is a drain point a few inches from the bottom of the tank in the cupboard, I have opened it for about a minute but only clear water came out is this the right point and am I doing something else wrong

Since you don't have a water heater and I'm not familiar with your hot water system let's get you back in business. You'll have to open up each faucet and clean out the crud from the cold water seat if a two knob faucet or the cold water inlet port in the cartridge if a one handle faucet. Good luck, Tom

Right I ll just update you to where I'm at, the water for the bath cold tap comes straight from a tank in the loft. This is the only pipe coming from the tank and is just a agravity feed, I've drained the tank and fed water through the pipes with a hose pipe and water flows through OK with the pressure from it. When I put every thing back together I still get only a trickle any ideas as to why thanks.

"ive drained the tank and fed water through the pipes with a hose pipe and water flows through ok with the pressure from it. when i put every thing back together i still get only a trickle any ideas as to why thanks."
Now that's downright weird! There's no doubt in my mind that there's a blockage. If I were there I would figure out a way to attach the hose to the spout on the tub. I would then drain the tank, open the cold water tap, turn on the hose and see what came out in the tank by back flushing the system.
Let me know, Tom