Forum Title: Cross Connection Crossover in Master Shower
I am unable to control the temperature in my master shower. Water is either scalding hot or goes cold. My water heater is a tankless Bosche. This problem has been going on for several years which I can somewhat mitigate by changing shower heads, but it does not work for long. Problem had vexed multiple plumbers. Initially, the shower diverter valve was replaced. Did not work. Later I replaced the whole fixture in the shower. No solution. No other fixture in the house is affected by problem, leading me to believe the water heater is not the problem. I found a bulletin released by Bosche on an old, old water heater sales site that gave possible reasons for the problem, one being a crossover of cold water into the hot water stream causing a backup to the heater, thus causing it to fire incorrectly, if I understood right. Sure enough, when the hot water is turned off at the heater, cold water still streams out of shower when turned on hot. However, plumbers still are not sure how to fix it. Plumber wants to replace cartridge again (which I think is a waste of time) since it has been done twice, the move on to replacing the washer solenoid. I have read washer solenoid could problem, but I do not know how to prove it. Also, when I cut off valves to washer, crossover still occurs. Does anyone know how to test if washer machine is causing problem, or does anyone else have any other brilliant ideas of where a crossover can occur?
Category: Plumber Post By: CHRISTY BALL (West Hollywood, CA), 10/29/2016

Arrow is pointed up. It is a shower only so other spout is closed off.

- TERRY KLEIN (Racine, WI), 09/15/2017

look and see if showervalve was installed with the shower head as spout and spout as shower head valve has either arrow pointed up or H C SHR

- WADE FRANCIS (Glendora, CA), 09/22/2017

Do you have any 2 handle faucets in the house?Shut off cold supply to water heater. Open hot only on a 2 handle faucet. No 2 handle faucets?? Then shut cold angle stop off to a faucet so you know 100% that when you open that faucet you will only get hot ( if Hot was on at heater ) You should have ZERO water flow from that faucet. If you have water flow, then YES you have a cross over some where. Let the faucet run. make sure the drain can take it before you walk away. Now go listen to the other fixtures ( Closed ) for water passing through them. Older style MOEN's are known for crossover problems but mostly when the hot and cold systems are unbalanced. The auto washer. turn off the supply valves and disconnect the hoses to make sure the valves do shut off 100%.

- TYRONE MCCARTHY (Simi Valley, CA), 10/03/2017

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