Hi all,

Hoping someone can help me figure out one issue that has recently started in my home, and one that has been occurring since purchasing the home - unsure if the two are related.

I have two bathrooms on the second level of the house - bathroom A and bathroom B.

The sinks (two) in bathroom A are single handle lever types where all the way one direction is full hot and all the way the other direction is full cold.
The shower in bathroom A is single rotary style handle. The shower is a dedicated shower, and does not have a pull stopper like on a shower/tub-in-one.
Bathroom A has a dedicated tub, with separate rotary knobs for hot and cold.

The sink (one) in bathroom B is a single handle lever type where all the way one direction is full hot and all the way the other direction is full cold.
The shower in bathroom B is a single rotary style handle, and is a shower/tub-in-one, with the pull stopper to direct the water from the tub spigot, up to the shower head.

Ever since purchasing the home, we have noticed that after taking a hot shower in bathroom A, the water from the cold taps on the sinks in bathroom A runs very warm for a while, until the cold water eventually starts to flow. This occurs on both sinks in bathroom A. It is not just warm, like the water has been sitting in the pipe in a warm house for a while - it is borderline hot. The shower had started to aggressively drip, and I replaced the mixing valve cartridge. This fixed the drip, but there has been no change in the sinks, and we still get very warm water coming out of the cold sink taps for a significant period after running the hot shower.

Bathroom B has recently not been getting hot water from the tub. We turn the handle to full hot, and let it sit for many, many, minutes, and when we come back, the water is still cold - not even a hint of warmth. If I turn on the hot water in the bathroom A tub, even for just 10 seconds or so, by the time I can walk back over to bathroom B, the water coming out of the bathroom B spigot is hot. (The water at bathroom A tub is piping hot in a matter of seconds). I have tried opening the sink in bathroom B to full hot, and I get piping hot water in a few seconds, but no matter how long I leave that open, the water in the bathroom B tub never changes to hot. This issue started to occur after changing the mixing cartridge in bathroom A shower, but not immediately after - many weeks passed, so I’m not sure if they’re related.

Not sure if the following are relevant, but figured I’d mention them:
We have a whole home water filter and softener, but the bathroom A problem existed prior to its installation, and the bathroom B problem did not start anywhere close to post-install.
There is a hot water expansion tank on the water heater.


I’m flummoxed, and hope someone can provide some guidance as to what could be going on!



Edited 1 times.

Whew! That is a lot of detail to take in. And I don't have an explanation.
Turning on tub A brings hot water to tub B. What happens if Tub A is now turned off? Do you lose hot now in tub B?