We had some work done on the mains cold water feed into the house. At first everything worked just fine but after about a day when the top floor shower is now switched on there's a rapid banging noise and reduced hot water flow. Switching the cold water on, just a bit, in the basin next to the shower stops the banging but the hot water flow doesn't increase. The hot water flow from the tap in the basin (and every other tap in the house) is excellent.
What would cause this? Is it trapped air? Is the pressure too high for the shower?