We recently installed a new hot water heater. Now, if someone is in the shower and another faucet is turned on or a toilet flushed, the shower water turns extremely hot or very cold - This never happened with our old water heater. Any suggestions?

Your shower needs an anti-scald or pressure balancing type valve. Do a search on that on the search tab here.

Will that prevent the shower from turning cold also? Thanks so much for the help!

The new heater could have flow controllers in the inlet and outlet pipes that are reducing the effective pressure and causing the pressure imbalances when other items are used.

It's a temperature problem though, not a pressure problem - Do they both result in the same temperature changes/imbalance? How do we fix it? Thanks for your help!

I'm with hj on the restricter theory..something is different to cause a problem that was non existent before..unless the plumber used a stop type valve which can reduce flow..you can reduce the flow pressure quite a bit before you can feel it at a fixture with flow restricters in them, as all do...at any rate a pressure balanced valve will solve the problems of gettin scalded and ..yes..frozen

You have a pressure problem. The temperature problem is just a symptom.

Thanks again for your help - so is the pressure valve something that I can buy and install?

Most have the pressure balancing built into the valve so you would have to open the wall to replace it. There are "remote" pressure balancers, but unless the pipes to the shower are accessible in the basement, or attic, they also require that the wall be openened, but have less chance of also requiring tile repairs.

If both of our upstairs showers are affected, would this mean that the problem w/ pipes is closer to the water heater, or that neither shower has a pressure balancing valve?

The best thing you can do is call a Plumber and have them fix your problem.

if either had a pressure balanced valve..you wouldnt experience the problem

if this is a new problem with a new heater,let's start there. are the hot and cold hooked up to the correct sides?did the plumber melt the dip tube by soldering too close to the heater inlet?food for thought.....

The problem can be anywhere in the system, but if you bought a "good" water heater with a self cleaning feature that is probably your problem. It would be logical to assume that an installer would not have installed just one pressure balancing valve.