Hi, I have determined that cold water is entering my hot water lines and would like to try and identify where this is occuring. I believe this is what is happening because when I turn off the cold water input to my water heater (I have a tankless, on demand water heater), I still get water when I turn on a hot faucet. Also, my hot water is just not getting very hot. Is there any way to easily determine the source of the problem? I recently replaced my bathroom faucet and that did not have any effect. All ideas are welcome.

thanks!

 

jbl1120, Welcome to the DIY Forums.
Try going to each fixture and turn off the cold water supply valve under each. Do this one at a time. While the cold water is off, turn on the cold faucet on that fixture. This will determine if you have another bad faucet should you get hot water out of it. Good luck.

 

I did as you suggested and turned off each cold valve and checked the cold faucet, one at a time. All of them seem to work, that is, nothing comes out when the cold is turned off. I couldn't check the shower though, as there is no turnoff for that one - the problem could be there. Any other thoughts? Thanks for your help.

 

It may be the tankless heater is just not working properly. I have no experience with these but see a lot of complaints here in the forums about them. Of course, you have to realize that what we see most here, is complaints so don't totally rely on that. Good luck.

 

Hi, Are you sure the valve to the hot water supply is shutting the cold water completly off? Make sure when you turn on a hot water faucet with the supply shut you allow enough time to drain the pipes.Also shut off the valves to the washing machine. I would also shut off both hot and cold angle stops and would not turn them on untill you have tm all shut off ie shut the kitchen sink then check shut off bathroon sink then check again ect.
Good Luck Woodbutcher

 

I did a more thorough check. Turned off supply to hot water heater. Then went through the house, faucet by faucet (incl. laundry), turning off hot and cold angle stops. I made sure to leave enough time for water to drain from system. When the hot supply is turned on, it continues to run indefinitely. There must be cold water getting into the hot lines somewhere. My faucets are all quite new. The only one I couldn't check is the shower.

I'm thinking at this point I just need to call a plumber to check it out. But before I do, can anyone elaborate on possible causes of the crossover? I have received some helpful advice but nothing that validates the crossover as the situation that this sounds like. Thanks for all the assistance!

Justin

 

Several questions come to mind. What type of structure is your home? Slab or peer and beam, What brand and model is this heater? I would have to agree with woodbutcher, the main cut-off valve at the water heater is probably not closing completely. How old is this home and when did you first notice the problem? More often then not a direct cross connection is made at a piping manifold in close proximity to a plumbing fixture. The easiest way to confirm this is to get a thermometer and check the temperature of the hot water at each fixture. A variance of more then fifteen degrees cooler then other fixtures would be a good indicator of a cross connection in the manifold suppling that fixture. Let each fixture run for at least 30 seconds before recording the temperature to insure maximum heat reading. This is sure one of those problems most plumbers would rather see then read about, it’s just hard to diagnose with out seeing the whole lay out. Well, post back and let us all know how it turns out.

 

House is not on slab, it has a crawlspace underneath, pier and beam. The heater is a Bosch AquaStar 250 - it is 6 months old, I installed it, and installed the shutoff valve at it's entry point, and I believe the valve is completely closing when I test it - it certainly feels like a good valve and I cannot detect any water running through the heater when the supply is turned off. House was built in 1917, but plumbing has been upgraded to all copper lines at some point. I first noticed the problem a few months AFTER installation of the water heater. The only other work I did was to install irrigation system in backyard (cold water lines only of course).

I will check the temperature and report back. I suspect it is the shower faucet/knob, as that is the only older faucet in the system. Will report back!

 

By any chance do you have a tempering valve on the supply to the toilet? This is a valve which mixes some hot with the cold supply to help with condensation on the tank. If faulty, such a valve could be you problem.

Also, what brand is the shower? I have heard that old Mixets had a crossover problem.

 

I had some old moen shower single cartridge facuettes that were the casue of that very same problem. Replaced the cartridges, still had problems. Replaced the fixture and the problem was fixed.

 

Just want to thank everyone for the helpful insight. I got a new Price Pfister cartridge for my shower fixture today, and it seems to have resolved the crossover issue. I can't wait for tomorrow morning so I can take my first truly HOT shower in many weeks!

Thank you, this was a very helpful resource.