Shower Cold, plumbers clueless

[AWK]

shower cold unless hot sink or bath tap turned on for a few seconds.
shower then remains hot for about a minute then goes cold.
Original shower Mira minilite evs, replaced with an Aqalissa bar type....
still same problem. Using a megaflow unvented system with mains cold direct to shower, spoke to a plumber on phone... he aint got a clue..HELP.

 

[Riley]

Go us

 

[AWK]

how do I give you guys a rating?

 

[Riley]

Badges below each post

 

[Aire]

Go to the top of the class CBW1982 AND RILEY, mixer tap in bathroom sink causing problem... isolate one side and water out of both. just had a hot shower YIPPEE. Thanks guys.

You do realise that @townfanjon suggested this an hour after you posted your question, and you dismissed him straight away saying your other taps were fine. Try listening to the experts next time your given good free advice.

 

[AWK]

I do apologise townfanjon, missed that. u just got a winner tick.

 

[townfanjon]

I do apologise townfanjon, missed that. u just got a winner tick.

Shakes his head , lol . I will pm you my bank details.