Andy Frank wrote:

I have a Master addition on my house that has a Master Bathroom.
Everytime you are in the master shower and someone flushes the master
toilet, the master shower scaulds the person in the shower. The
scaulding water has to be from the toilet taking too much water from
the cold water supply line. What are the obvious reasons? I think the
toilet is an old 3 gallon toilet which might consume too much water,
but are there other reasons? Is the cold water supply line to the
Master addition too small?

Any help or ideas is much appreciated!!!

Andy

Size of toilet has nothing to do with it.
Shower control should have been a "pressure-balance" type or
scald-guard (temp compensated).

You would need to know much, much more about the system to
pinpoint the cause though.
City/well water? Pressure at the supply?
Age and type of supply piping in the original part of the house?
Type of water heater? If a coil in the boiler without a
storage vessel, this setup is very prone to scalding and should
have a thermostatic tempering valve.

With so many variables, you probably need to have someone local
who is experienced look at it.

Jim