Hot water only when two taps on!

[dave_n]

Hi
I have a vaillant combi.
Central heating is working fine.
If I put a tap on for hot water the boiler fires up but only delivers luke warm water.
If I leave the tap on (tap A) and then go and turn on another tap in the house (tap B), then tap A delivers proper hot water!

Any ideas at all?

 

[Plumbstar Tom]

has this always happened?

Are these new taps?

 

[dave_n]

Hi Tom

only started yesterday....taps have not been changed for years...in fact nothing has change.
No leaks anywhere, pressure is fine on boiler (1.2bar)...
Boiler is a Turbomax

 

[Plumbstar Tom]

may be a flow switch on boiler

 

[dave_n]

one for an engineer or something I could sort?

 

[Plumbstar Tom]

Would never recommend DIY on a combi im afriad

Its Gas

Its mains pressure Water

Its Electricity

IMHO