"Andrew Collins" wrote in message
...
I've been hoping to install a mixer shower, the problem I have is this
- the boiler (Worcester-Bosch 240) if fine for CH, but will only heat
DHW if the tap is fully on. If it isn't, or another tap in the house
is in use, the boiler will shut down.

Discretion being the better part of valour I bought a udder type mixer
shower just to check to see if it would work, and it won't. The boiler
just about fires up with the hot tap only on, but touch the cold tap
and the boiler shuts down.


Thanks for your help!
-Andrew

--
Andrew Collins
That boiler should be just fine with a mixer shower that states its suitable
for use with combi boiler.
It seems that back pressure from the cold feed to the shower valve is going
into the boiler h/w output and so stopping the flow.
These valves often come with various restrictors that you put in either feed
to even out the flow.