We have a problem with the cold water flow as it just trickle out. The hot water flow is fine. We have the Combi Faucet 6310 series

Check for restrictions in the shutoff valve and the stem of the hot water side.

Boilers are inherently dangerous for the average DIY for so many reasons, contact British Gas and have them come back and fix it, tell them it was fine before the "service". They may simply have a control valve shut off.

With posi-temp cartridges, if one supply of water, hot or cold, is interrupted, the cartridge automatically restricts the flow of the other water source. This is to prevent you from getting scalded if the pressure on the cold side drops because of a toilet being flushed or any other uses of cold water. The cartridge will only allow cold water to flow through if there is hot water to balance it out. If you restore hot water to the faucet, it will operate properly.

You have already checked the two obvious things now make sure the two supply lines from the shut off valves are not kinked or turned it such away as to close off the water flow. If that is ok then there may be some debris in the internal filter screens.

Keep in mind that this faucet design will not put water out at a high pressure if it did it would splash all over the place.

It says you have a problem with the hot water. First thing to do is to turn the hot water supply valve under the sink off, and then remove the line from the valve to the faucet at the valve. Then put a bucket underneath the valve and turn it on (carefully). If you don't get any flow, then the problem is in the valve or the pipes supplying the faucet. If you get flow there, then the problem is in the supply line or possibly at the faucet.

If water come out the faucet hot line,check if is clogged.For this job you need to disassemble the faucet.

Here is a good PDF source to do it.

If you need more help come back.Post / thumbs / testimonial are welcome!

Yes, you need to replace it.

your problem can be fixed by running a loop in the plumbing. If you hired a professional in the first place it would already be done. basically the water pressure isn't enough, i bet your faucet is on the second or third floor, or even just THAT far from the water heater.

if this is the faucet in picture, turn off water, pull out cartridge and inspect for any debris in cartridge or valve body, if not, turn on hot water to see if water is getting through valve body. May have kinked line or debris from or in angle stop line.

Usualy when this happens you need to change out the cartrage that controls the water. try to find your faucet at the link below. If you find it click on it scrol down and you can view the manual. It will terr you how to change it out.

http://www.deltafaucet.com/bath/index.html#tubshower_

Good Luck