In the bathroom of this rental is a tub with a shower diverter. It's an older setup with a hot & cold faucet and a center valve (one direction diverts to shower, the other to the tub faucet).

If I turn on only the hot water, I get hot water for 30-45 seconds, then it goes cold. The water is heated by a stove oil fired boiler which also heats the building via radiators.

If I go to the bathroom sink, or to the kitchen sink and turn on only the hot water, I have hot, hot water for virtually as long as I keep the faucet on.

One additional issue is the water temperature is set way too high. At the kitchen faucet, I measured the temp, and after about 30 seconds, the water temp stabilizes at about 185 degrees.

Too high, seriously dangerous too high, but the landlord insists the boiler has to be set that high, or "there won't be any heat in the winter, and everyone will complain about THAT."

This same landlord also argues with me that insulating the supply pipes to the radiators 'wastes' the heat in the pipes, and has forbade me insulating them in our apartment, even though they are a serious safety issue.

I don't see how the high temp setting would cause only the bath tub to have limited hot water, but after seeing what the hot water did to the drain pipes in the third floor bathtub, right above our second story bathroom, I'm wondering if the 185' water has damaged the diverter. [We have a suspended ceiling in our bathroom. A leaky hot water faucet in the 3rd floor bath tub leaked 185' water into the PVC drain pipes, causing them to deform, then leak, then soak our fiberglass paneled ceiling, (like in a typical office), which then caved in at 6:00am one morning.]

He ended up paying me to fix the plumbing and ceiling, and in 40+ years of construction, I've never seen anything like it. I had to replace everything from the strainer on the tub to the junction with the 3" cast iron vertical drain. It was all distorted and melted from hot ass water.

Anyway, we have the 185' water, and still have to take cold showers most of the time because of this strange issue with the diverter in the tub.

I have tried every combination of adjustments, but can't figure out what's wrong. When I take a shower, I've noticed I get MORE hot water, if I open the cold water faucet further, but at some point, it doesn't help.

Any ideas? Wild guesses? Could the 'clowns' have installed the diverter incorrectly? It's been replaced in the last 5-10 years, from what I can tell.



  • 1
    Does the hot water system have a recirculation pump? The strongest hint that there is would be if the hot water is available within a few seconds when opening a tap after no hot water use for hours.
    – wallyk
    Apr 19, 2017 at 6:06
  • I don't believe it does. I haven't seen an obvious pump near the furnace/boiler, and it can take 10-15 seconds to get hot water out of the faucet, if it hasn't been used. The 185' temp was after 30 seconds, where the temp peaked.
    – GeoNOregon
    Apr 20, 2017 at 14:45
  • Anything above 120F will scald you. You need an anti-scald valve installed ASAP, and one that is rated for 212F because if you do have one it is clearly not capable of handling 185F or it has an over temp safety feature. If the landlord won't install anti-scald everywhere. This is a legal liability to the landlord. Get scalded, sue and win big, but be sure to document everything with a video camera and several different thermometers. You are not supposed to provide hot water from the hot side of a heating furnance!! you need a water heater!!
    – cybernard
    Dec 11, 2017 at 23:04
  • 2
    If you know it's too hot and still get scalded, you have no case. You're not allowed to scald yourself on purpose to get a payday. OP you're in construction, you surely realize that anti-scald valves exist, and it sounds like you are amply capable of both plumbing and drywall. Nowadays now that we know legionella grows in water heaters, everyone's hot water is scalding and everyone needs anti-scald valves. I also think an anti-scald valve will fix the shower as I think it's a differential pressure problem. This for sure: don't be inthe shower when a pipe burps and you get a slug of 185F! Feb 16, 2018 at 17:56
  • 1
    This seems a little crazy... perhaps there is an anti scald valve already there that is malfunctioning, or can't handle the 185 degree heat. I have boiler heated hot water in my house, but more modern - a regular tank heated with a heat exchanger and a thermostat. It seems to me, that this is your landlords problem, you don't have hot water - that's something he needs to fix. It is also dangerous. 185* can put you in the hospital. I hope there are no small kids in the house.
    – slambeth
    Dec 5, 2018 at 16:27

5 Answers 5


You are pretty hardy if you can take a cold shower in NY in the winter or spring . . . or even summer. We have the exact same old fashioned tub/shower with old Price Pfister separate hot and cold valves with a diverter in the wall on a line between the hot and cold handles. I have taken this type of tub/shower valve apart and they are pretty simple. I do not see how any problem with the diverter could cause cold water to come from the hot water line. What do you get if you turn on the cold water valve and leave the hot valve shut?

Are the cold and hot pipes connected by an anti-scald device?

Some models of anti-scald mixing valve are designed to be placed at the output of the boiler, but others could be just upstream of the shower. The fact that the lavatory delivers hot water continuously as expected but the shower does not, could be due to the presence of a hidden mixing valve in the wall behind the shower. The scenario would be that the hot water is so hot that it drives the valve to the cold stop.

Try turning on the shower cold water valve first to a moderate or high flow and then metering in increasingly larger amounts of hot water to get to warm. Maybe a relatively high flow rate of cold water from the beginning will prevent the thermostatic mixing valve (if there is one) from being over heated and over driven to the cold stop.

  • 3
    I have no personal experience with a combination boiler which supplies both hot water for space heating and domestic potable hot water. But it seems clear that if the heating system requires 185 F water, that there should be a thermostatic mixing valve at the boiler which mixes in cold water to keep the temperature in the potable water system at less than that, say 140 F. Like this media.wattswater.com/ES-1170-L1170.pdf Apr 19, 2017 at 8:58
  • I just learned yesterday the upstairs neighbor is having the same issues with her shower & other faucets.
    – GeoNOregon
    Apr 20, 2017 at 14:46
  • (Oops, hit return) When I first measured the water temp & researched this last Summer, I learned rentals in NYC, proper, are mandated to have thermostatic mixers at ALL hot water faucets. I assume it is because of the prevalence of old buildings with boilers. I don't believe the system NEEDS 185', from what I have learned.
    – GeoNOregon
    Apr 20, 2017 at 15:00
  • Well does this building have thermostatic mixer valves on the showers? have you tried to use the shower by doing what I said above, namely, first turn on the cold at significant flow then meter in the hot in stages to bring the shower to warm for showering? Apr 20, 2017 at 20:22
  • 2
    If these showers could suddenly spray someone with 185 F water, this could cause absolutely ghastly injury. If there is any possibility of this happening it is unacceptable, even illegal. In my jurisdiction AFIK kitchen faucets and lavatories are not required to have thermostatic mixing even though showers now are. In general it might make sense to allow hotter water to emerge from say the kitchen sink, but I know one person who washes a small dog in the kitchen sink. I wash our dog in the tub/shower, where full hot from our tankless heater is about 120 F. Adjustment to lukewarm is stable. Apr 20, 2017 at 20:51

The issue is probably a thermostatic valve on the 'showers' line that is set too low or simply is broken. (my boiler has one that fails and have to be replaced about once every 5 years) PS: 85°C is a common temperature for radiators and also for storage hot water if the tank is small (with lower setting there won't be enough water for all). Hot pipes are not a big issue: you simply won't be able to touch them for longher than few 10th of second, also some heating systems require them to be un-insulated as rads are sized considering also the heat released by pipes so insulating them may result in cold room.


The heater may need a minimum flow rate to go with the water temperature.

If that is the case, then running the hot faucet in the basin at the same time as you take a shower may work. You might need to run the cold faucet too to avoid heat damage to the basin drain. Yes, it is wasteful, but at least you will be able to shower in water at a reasonable temperature.


Seems to me that you need to call the building and safety department in your jurisdiction. That should take care of the whole problem.

  • Probably been sorted already given the original post was April 2017...
    – Solar Mike
    Mar 3, 2019 at 7:42

My boiler is set at 185, just the way house works. The boiler makes on demand hot water has own coil, and a dual aquastat .The hot water exits the hot water coil. Then went through a mixing valve witch you adjust to temp. I keep water a bit high, like it hot at kitchen sink. Then the shower has a anti scalding . It never was a problem . When i had kids. I put in those scolding shower heads. Hope this is helpful . You do have some thing wrong hope its not straight boiler water.Sounds like boiler needs mixer or just simple adjustment. And shower needs work new shower valve.

  • Hello, and welcome to Home Improvement. There may be good info here, but it's really hard to read so few people will benefit. Would you spend a little time editing and cleaning up, so people can learn from your knowledge? Thanks. May 22, 2019 at 12:39
  • Yes I need help on that seems to get me in trouble .The points i am trying to make are.The boiler at 185 normal, a bad mixing valve at boiler. Or no mixing valve at boiler witch makes this real bad. I will put time in to clean up post,may take a bit type one finger at two words a minute.
    – user101687
    May 22, 2019 at 16:19
  • Thanks for working on it; we'd love to have your expertise. May 22, 2019 at 17:16
  • Did my best ,Grandsons at school takes him seconds to type .
    – user101687
    May 22, 2019 at 17:33

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