hot water keeps cutting out on combi system

[obseen16]

hi all,
i replaced a kitchen tap for a customer this morning, it was a like for like tap same model etc, after fitting this tap i tested it and it worked fine pressure was good on hot and cold. however i got a call this afternoon from the customer about 5hours later saying she has no water in any taps. i called round and took a look. the cold water runs ok but if i turn the hot tap on it will run hot water for about a minute and then dribble to a stop. i checked the taps in the bathroom and the cold runs okish. i turned the hot tap on in the bathroom and it ran, i then turned the cold tap on and the hot water stopped dead. to me this seems like it could be that their is temporary low pressure in the mains. or could it be a boiler problem? (system is run off a combi not gravity fed).

or could it be something else???

 

[obseen16]

customer thinks it could be something to do with the stop tap as cold pressure "isnt as good as it normally is".
the inside stop tap didnt turn very much at all so i used the external stop tap at the property boundary. could i have dislodged anything in the inside stop tap??? i only turned it quarter of a turn before it became stiff and then turned it quarter of a turn back. cant see that causing the stop tap to cause a blockage.

 

[obseen16]

thanks for that i advised the customer that it is possibly the stop tap. however the customer has decided to try to change it himself which is fair enough. hope that sorts his problem out. thanks for your help AJS.