hot cold temperature

Hi,
I hope someone can point me in the right direction. I live in a huge apartment building. The shower is constantly turning from hot to cold. 1 minute hot 5 min later burning sometimes cold but mostly hot issues. I got a plumber to look, and said it had to be the cartridge. He changed it. In the meantime we had changed it before problem not solved. It is an old shower system which does not have a built in temperature control. I checked with the building and they said it cant be the lines. Our next door neighbor on the right and left have the same issue but not upstairs nor in front of our apartment. There was a suggestion it could be an illegal washer hooked up somewhere but I cant get the building to investigate. It is so frustrating. I dont want to spend money on a new shower control and then it turns out to be something else. Any suggestions. Thanks

One possibility is one of tenants has a hose sprayer kitchen sprayer with an on off control at the head. Or someone with a washer hooked up with hot and cold combined with a tee before the washer. In other words, there is an open connection between the hot and cold piping that allows hot water to flow to the cold side. Probably with one of the effected units.

With it happening with more then one tenant its not the shower valve.


So why does the management say it can't be the lines. With multiple tenants having the same condition it really could be a cross connection somewhere.

How old is the building. I'm assuming the building has a common hot water system, which for a larger building is quite common. Another possible issue is the hot water return is piped wrong at the water heater and allows hot water back into the cold water side.

That's not that uncommon either. Could be caused by a bad check valve on the cold water supply to the water heater if the building is older too. I would have the management have someone out to check the water heater system and hot water return pump/piping. If there is hot water before the check valve at the water heater then the check valve has failed.

If they have a master thermostatic mixing valve at the water heater then that valve could be defective too.. So YES it could be the piping system too.

thanks Beni for the information. I will investigate further. The management said it cant be the lines because the line we are on is up and down and the apt directly above us does not have the problem nor below. Only left and right of our unit.
Thanks again

How tall is the building and what floor are you on. Also are the water heaters serving the building or pressure zone at the bottom or at the top of the building. Also how old is the building and is the piping copper or galvanized steel

While the hot and cold for the units feed up vertical (which is pretty standard BTW), normally the hot water returns are connected at top of each pressure zone in a high rise building. It is possible that there is unbalanced flow is in the hot water return, which is why it may only be on certain floors.

So yes it still could be related to the hot water return effecting units, specially if your unit is on the top floor of a pressure zone. Gee it could even be caused by a cross connect between the hot and cold water somewhere. That also happens from time to time and really hard to track down.

Normally in high rise buildings the water systems are split into pressure zones of somewhere between 10 and 13 floors (depending on the floor to floor height). That is done so the units at the bottom of the pressure zone don't exceed 80 psig.

It is very common for the hot water returns to be collected at the top of the pressure zone. So for that floor its quite possible that some units side to side can be effected by adverse water flow. Very tricky to check out too

One note, Some systems are designed to feed down. For those buildings the hot water return collects on the lowest floor of a pressure zone.

BTW I've designed quite a number of high rise buildings. So yes it still can be related to the building piping...

Beni Bacon, PE, CIPE