I have recently had a new Combi boiler fitted and when any of the HOT water taps are turned on there is weird noise squeacking/groaning that can be heard around the house.
It only happens on the hot water and goes away when the tap is turned further on or a cold tap is turned on.
The noise sounds louder in the upstairs back to back bathrooms,
The pumber says that there is nothing wrong with the boiler.

Any ideas how to fix this, thank you for your replies j

It is usually caused by the fixture you turned on,also make sure angle stops are all the way on under the sinks.Also you can disconnect and check the hot supply lines at the faucets for sediment or obstruction.You should try to use your ears to determine where it seems to start.Back to back bathrooms, sounds like an older home and may have galvanized water lines where sediment will always be a problem.Usually the noise is caused when you have faucets that plastic type valves or cartridges that will vibrate when the flow is obstructed.Also make sure your Fixtures are not leaking hot water,like tub valves and such.If so you need to repair them as that can also cause noise.

I would agree with Plumb382 about it being in one faucet except the OP stated:
when any of the HOT water taps are turned on there is weird noise squeacking/groaning that can be heard around the house.
Noise is caused by vibration. Somewhere the noise will be the loudest and the vibration will be the strongest. We don't have combi boilers in my area but that's where I'd start checking. Perhaps one of my Yankee friends can give you likely areas around the boiler to start checking. Good luck, Tom