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?
Update: It turns out that a little piece of plastic had worked it's way up to the shower and got trapped in the hot/cold water mixer. Took a plumber about 1 minute to pop the cap off, clear out the mixer and put it all back together. Sorted!