Toilet flushing & Hot Shower

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
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Andy Frank wrote:

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
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Don't they sell some sort of auto balancing valve to prevent this that can be installed?

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How old is your master bath?
First the shower valve to reduce or eliminate the problem unless it is really old. Second if the supply was designed right and working right, it would not be a problem. Note: Speedy is on the right track asking the questions he asked; they are the start of finding the problem and the solution. One last suggestion. The supply line to the toilet should have a valve on it. Closing the valve part way will reduce the problem until you can have it resolved. Don't think this is THE fix. Next time someone starts brushing their teeth the same problem will still be there.
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Joseph E. Meehan

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Cutting back on the tank supply valve has become the permanent fix on many.

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Yea, you're right, but it is not a fix. ;-)
--
Joseph E. Meehan

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C'mon, buddy. Sometimes we are too much of the purists for our own good. The supply line is big enough to supply sufficient water delivery speed for the big tanks. Now we have 'tiny' ones. Cutting back on the delivery speed is not so bad. Something to appreciate when things get plugged up and there's still a delivery through the overflow tube. Ya know, a twist tie around a couple of parts can be a fix. Not elegant, or even esthetic. But it can indeed be a fix. As can be a reduced delivery to the tank to keep folks from getting that 'there went the cold water' feeling. I say turn the tank temperature down to the point that cold admixture is unnecessary.

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I am not at all worried about the toilet. It would appear the real problems are a cold water supply that is inadequate because it is too small and/or insufficient supply (pump?) and/or restricted and the lack of an anti-scald valve. The real fix is to address those issues.
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Joseph E. Meehan

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<< has to be from the toilet taking too much water from the cold water supply line. >>
Restrict the bathroom to one occupant at a time. Problem solved.
Joe
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