We have a unit upstairs in a 4-plex. The other units don't have any issues, but hot water recently stopped working in this apartment. Rarely water might get hot or warm but goes cold again. When the plumbers came and we played around with the fixtures we found out that the sink in the bathroom would get hot if the shower was on. When we turned off the shower/tub water the sink lost heat. I believe it was the same with the kitchen sink, but I could not figure out when or how to get the shower hot. The plumbers were also dumbfounded but one thought something was wrong with the shower cartridge so we replaced the entire faucet set including the rough in valve. I'm not sure how that would effect the other fixtures, but regardless it did not help.
Also we noticed that the shower handle was installed backwards once again (part of the reason the plumber thought it was the cartridge) i.e. the valve is off when it is supposed to be hot and vice versa, but how could that be causing, or allowing the other fixtures to get hot water? Won't reversing the valve still mean that the other fixtures will still be dependent on that valve when they should be independent from it?

We've already called several of the best plumbers around, and no one seems to know what's going on. The possible explanations make sense individually but not together. The water heater can't be broken because there CAN be hot water. If something is wrong with the way things were piped, why would the problem only occur now after so many years? The fact that the sink gets hot when the shower is on is what I think confuses most people. I will try playing around with the temperature limiters, but I assume it will not help, because again, why would one fixture affect the other ones?

I hope someone can provide some sense or help us troubleshoot the problem. We've already spent quite a deal of time and money and our tenants are getting annoyed. Thanks!

I'm not a plumber so will just guess til they get here: mineral build up in the hot water to the bathroom somewhere in the wall.

Need a little more information, OK?

Are all sink faucets single handle faucets? If not, how many handles are at each faucet... please provide info. For every faucet/valve in the house.

Is there a washing machine in the unit? If so, is it a single lever valve or does it have separate shut off valves?

Has anyone tried closing all the cold water valves ONLY under each sink and then test for hot water at each fixture?

In most case like this there is a SINGLE HANDLE valve (or faucet) that has a mixing cartridge that has gone bad and is allowing hot (or cold) water to flow into the cold water (and vise versa). Once we identify the exact faucet or valve (the other guys GUESSED the shower valve), the problem should be pretty easy to resolve.

Back to you...

Mark

My guess would be that there is a hot water recirculation line. In other words, a line from the furtherest point on the hot water piping, back to the water heater cold water input side. I would think that such a recirculation line in a 4 unit apartment building would have a pump to keep the hot water circulating. If there is no recirculating pump it would be a gravity recirculation line. If recirculation line has a pump it is faulty. If there is no pump and it is a gravity line, the check valve is failing.
Opening one faucet would allow the cold water to flow through the recirculation line. Opening two or more faucets would would cause the cold water to flow, but the also cause enough pressure difference for the hot water to flow from the water heater and mix with the cold.

Need a little more information, OK?

Are all sink faucets single handle faucets? If not, how many handles are at each faucet... please provide info. For every faucet/valve in the house.

Is there a washing machine in the unit? If so, is it a single lever valve or does it have separate shut off valves?

Has anyone tried closing all the cold water valves ONLY under each sink and then test for hot water at each fixture?

In most case like this there is a SINGLE HANDLE valve (or faucet) that has a mixing cartridge that has gone bad and is allowing hot (or cold) water to flow into the cold water (and vise versa). Once we identify the exact faucet or valve (the other guys GUESSED the shower valve), the problem should be pretty easy to resolve.

Back to you...

Mark

Thanks mark!

There is a single handle delta faucet in the shower and it was replaced with another single handle delta faucet set but it did not improve anything. Both somehow managed to be installed backwards.

There is one sink in bathroom and one in kitchen -- both are two handles one for hot one for cold.

There is a washer and dryer in the laundry room next to the building, where the shared water heater also is. I'm not sure about the valves on the washer but can find out if it's necessary. I'm just thinking it probably isn't pertinent if the other 3 units are working properly.

I have not tired turning off hot or cold individually but I wouldn't know what to look for if I did.

My guess would be that there is a hot water recirculation line. In other words, a line from the furtherest point on the hot water piping, back to the water heater cold water input side. I would think that such a recirculation line in a 4 unit apartment building would have a pump to keep the hot water circulating. If there is no recirculating pump it would be a gravity recirculation line. If recirculation line has a pump it is faulty. If there is no pump and it is a gravity line, the check valve is failing.
Opening one faucet would allow the cold water to flow through the recirculation line. Opening two or more faucets would would cause the cold water to flow, but the also cause enough pressure difference for the hot water to flow from the water heater and mix with the cold.

Sounds like you really know what you're talking about. Conversely, I do not understand any of it. Is there anything I can look for or would we have to go into crawlspace/tear walls down?

Show this thread to your plumbers, it may trigger some ideas.

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