Poor pressure on combo hot water

[Gary newman]

I had a plumber in to change a basin and thermostatic shower in my bathroom, the flow coming out of my hot basin tap is poor but the water is hot!!! (Previously it was good) and the shower is hot for about 15 seconds then goes cold , the pipework is all correctly installed as he showed me before where he marked the pipes hot and cold, then showed me after he installed that hot was to hot and cold to cold , can anyone shed any ideas as to what the problem could be please

 

[Riley]

Is it all hot outlets?

 

[Chuck]

A simple explanation would be that a/the stopcock was not re-opened fully after it was closed to do the work. (Stopcocks should normally be fully opened and then closed by between 1/4 and 1/2 turn to prevent seizing.)

If this isn't the explanation, can you provide some more details about the installation (tank or no tank, vented or unvented, electric or mixer shower, etc.) and some photos of the plumbing, please? What about the other taps in the house, how are they working?

 

[Rob Foster]

Did you have new taps ? Or re-use the old ones
Centralheatking

 

[Aire]

He installed a new basin so did he re-use the same taps and now they're not performing as good? Or has he installed a new tap that doesn't have as much flow as the previous tap?
As for the shower, if it's only getting hot for 15 seconds this could be caused by unequal pressures, some showers are more sensitive to this than others so while your old one ran fine, your new one might not. As chuck mentioned, we need to know more about the installation. Combi, tank or unvented?
Your title says combo hot water so if this means your on a combi, your hot and cold water pressures aren't equal, showers that require balanced feeds will supply different restrictive filters which you place in cold feed to the shower, the instructions state which filter to use depending on the kw rating of the combi, if this hasn't been done then it could explain the issue your having.