House water hot and then cold

[LCF]

My new house is having issues with what I believe is from a crossed water line or the well pump/tank. If I am posting this in the wrong section I apologize.

I thought the issue was because of the 30 year old electric tank water heater so I replaced it with propane tankless on demand and the problem is still happening.

Each time any shower or sink is on and the water is nice and hot, at a certain point it will go cold for 30 seconds or so.

Today I tested it and saw that when the pressure tank is low and kicks the pump on, that is when the cold water starts and it stays cold until the pressure tank reaches max pressure turns off the pump and then the whole thing repeats.

I know this could be one of many things. I have had multiple plumbers out here and none of them want to help me find the source. It is probably a crossed pipe somewhere but the house is old and huge and I don't know how to figure it out on my own.

Would a cycle stop valve before my tank be a bandaid for this? I am hoping to renovate the house over the years and replace all the plumbing at some point but for now I really just want a steady and hot shower.

Thanks!

 

[Sylvan]

Shut the supply valve for the H W tank . Then open a faucet on the hot water and see if you have flow and if you do guess what "" YOU do have a bypass some place .. Good luck locating it POSSIBLY a Moen valve shower caused it

 

[Sponsor]

 

[Reach4]

I know this could be one of many things. I have had multiple plumbers out here and none of them want to help me find the source. It is probably a crossed pipe somewhere but the house is old and huge and I don't know how to figure it out on my own.

Weird. I don't see how a simple crossover could cause this symptom, but let's see what that crossover test turns up.

After that test, if finding and curing a crossover does not solve it, I would put a GHT pressure gauge on the drain for the WH, and see if the pressure at the WH lags the cold water pressure.

 

[Terry]

Sometimes a crossover occurs when there is a shutoff on a shower head and the valve left on.

If it's not crossover, then I wonder if a check valve on the incoming cold to the water heater would help.
A tankless water heater will have what they call a cold water sandwich, where water passes through and the the unit decides on how much flame to use.

 

[Bannerman]

Have you checked the air precharge for your well pressure tank? The precharge will be typically set to 2 psi lower than the well pump activation pressure. If for example your well pump utilizes a 40/60 pressure switch, the air precharge will be 38 psi which is checked and adjusted using a tire pressure gauge on the pressure tank Schrader valve while the pump is unpowered and the house plumbing drained to 0 psi (not necessary to drain water heater).

Although you said the issue was also occuring with your prior electric tank type WH, with your new WH being a tankless on-demand unit, it maybe shutting off the gas burner momentarily if it is sensing even a momentary reduction/loss of water pressure, which is likely to occur if the pressure tank precharge is set too high and equal to or above the well pump's pressure switch cut-in pressure.

 

[LCF]

Thank you all very much for the advice.

I turned off the water outlet valve on the tankless and it kept pushing hot water to the faucets for almost a minute and then stopped. I am assuming that is all of the water in the higher level pipes draining back down so I don't believe there to be a crossover.

When I bought the house a few months ago I discovered the pressure tank bladder to be empty which was causing problems. I installed a new 40/60 pressure switch, and set the bladder psi to 38. I just went and checked the psi again and it was 42 at first and then ran some water and it stopped filling at 52 instead of 60 and then the psi read 51. Maybe something us going on here which could explain why it was also happening with the previous tank heater?

Any ideas on how to figure out what is going on? Terry mentioned this could cause the gas to skip firing momentarily which could be the cause though I am not sure how that would affect the previous tank heater in the same way.

Thanks!

 

[Bannerman]

Cold water sandwich was why I asked about the pressure tank precharge pressure being too high

If the tank's pre-charge pressure is too high, pressure and flow could reduce momentarily until the pump is running to immediately restore pressure and flow. Depending on the sensitivity of the WH flow switch, water flow may not necessarily stop completely before the WH burner will be shut down. These reasons however do not explain why the same situation was occuring with the prior tank type WH.

Is your home equipped with a hot water recirculation loop to allow hot water to circulate either continuously or on a schedule through the home's plumbing and back to the WH so as to reduce the wait time for hot water to arrive at distant fixtures?

Recirculation loops typically rely on one or more check valves to ensure correct water flow direction to fixtures. If a check valve is stuck open, water could potentially flow in reverse from the cooler return piping back to the WH, to flow to fixtures that are in use.

Is any type of mixing/tempering valve installed that will mix cold water with hot water that is too hot so as to reduce the temperature of hot water exiting the mixing valve?

 

[Reach4]

I turned off the water outlet valve on the tankless and it kept pushing hot water to the faucets for almost a minute and then stopped. I am assuming that is all of the water in the higher level pipes draining back down so I don't believe there to be a crossover.

That would have been more dribbling than pressurized if from pipe contents.

When I bought the house a few months ago I discovered the pressure tank bladder to be empty which was causing problems. I installed a new 40/60 pressure switch, and set the bladder psi to 38.

That sounds right if the pump is a submersible pump (in the well).

I installed a new 40/60 pressure switch, and set the bladder psi to 38. I just went and checked the psi again and it was 42 at first and then ran some water and it stopped filling at 52 instead of 60 and then the psi read 51. Maybe something us going on here which could explain why it was also happening with the previous tank heater?

I presume you are talking about the air pressure rather than the water pressure. You always set and measure the air precharge when the water pressure is zero. If the water pressure is higher than the precharge, the air pressure and the water pressure will be about the same. If they differ much, that would indicate that one or both of the pressure gauges is out of calibration.

Although you said the issue was also occuring with your prior electric tank type WH, with your new WH being a tankless on-demand unit, it maybe shutting off the gas burner momentarily if it is sensing even a momentary reduction/loss of water pressure,

Interesting idea. LCF, if you can repeat the symptom, watch+listen to the tankless as the well pump turns on and off.

Would a cycle stop valve before my tank be a bandaid for this? I am hoping to renovate the house over the years and replace all the plumbing at some point but for now I really just want a steady and hot shower.

Yes. That would keep the cycling from happening during a shower after the first time. Still, even with cycling, that problem would be something that should not occur.

 

[LCF]

There is no recirculation loop in the house. I have a Takagi and followed the instructions to cap off the hot water inlet and bring my supply into the supply for the loop because I do not have one.

Unfortunately after my last post I drained the pressure tank and checked the air psi and it was 13. I filled it with air back to 2 psi below and now i have hot water for longer but it's still happening. With the tank empty of water I sloshed it around and could hear and feel that it was still heavy with water so I believe that the water in the tank and loss of air pressure from when I last set it might be the cause.

Would the bad pressure tank also have resulted in these problems with my last tank heater?

 

[Reach4]

With the tank empty of water I sloshed it around and could hear and feel that it was still heavy with water so I believe that the water in the tank and loss of air pressure from when I last set it might be the cause. Would the bad pressure tank also have resulted in these problems with my last tank heater?

I don't see how. The bad pressure tank could create a stutter in the water pressure, but that should have affected both hot and cold. Clearly you have established that your pressure tank is bad. Bigger pressure tanks are in limited supply right now. If you switched to a CSV now, you would not need to be out shopping for a new big pressure tank. Lowes seems to have some big A O Smith units in stock. Specs look good, but I don't have experience with them and haven't read comments from others.

Maybe the hot water tempering/mixing valve behaves weirdly in that circumstance?
I was initially thinking maybe the shower pressure balancing valve behaves weirdly in that circumstance, but you get that same effect from a sink.

Do you have any check valves in your potable water system other than what is down the well?

 

[LCF]

There are no check valves that I am aware if but I know there is one on the submersible.

I know that this is happening in all of the showers and there are several different valves. One of the plumbers told me that my shower didn't have a mixing valve and that it wasn't the problem.

I also just was running the shower and had someone also at the hot water heater and can confirm that during fluctuations of the water heater burner, several seconds later is when the cold water comes so perhaps the water heater is not firing properly because of these pressure fluctuations. It's been driving me crazy for months!

 

[Reach4]

I also just was running the shower and had someone also at the hot water heater and can confirm that during fluctuations of the water heater burner, several seconds later is when the cold water comes so perhaps the water heater is not firing properly because of these pressure fluctuations. It's been driving me crazy for months!

Cool. Seems pretty solved to me. Bannerman called it.

Maybe if you get your pressure tank working right, the WH won't freak out and shut down the burner.

 

[LCF]

Huh?

There's too much water pressure
Otherwise hot water will flow into the cold water pipes. Many experts believe that such a problem may be due to the thermostat in the immersion heater. The thermostat can fail and this leads to hot water overheating and boiling over into the cold-water tap, making the stored water warm.

 

[Sylvan]

There's too much water pressure
Otherwise hot water will flow into the cold water pipes. Many experts believe that such a problem may be due to the thermostat in the immersion heater. The thermostat can fail and this leads to hot water overheating and boiling over into the cold-water tap, making the stored water warm.

WATER = Aquastat

The air temperature in a space is controlled by the thermostat the water temperature in a water heater or hydronic boiler is controlled by the Aqua stat

On a steam boiler we use a pressure stat

To prevent stratification of HW entering a C/W line the easiest way is installing a 27" loop on the CW supply a more common way is using the nipples usually supplied by the manufacturer and one of the worst ways to prevent the HW molecules from entering the CW line is using a check valve

Regarding too much pressure or temperature the T&P would discharge from pressure exceeding 150 PSI or 210 DEG F

 

[Valveman]

I don't know why this would be happening with the old tank heater. But we use Cycle Stop Valves a lot to stop the cold water sandwich for instant heaters. The 40/60 band width of a regular pressure tank means at 60 PSI the shower head delivers more flow and the flow switch in the heater stays up and the heater on. At 40 PSI the flow in the shower head decreases enough to let the flow switch drop and the heater goes off. When using a Cycle Stop Valve the shower pressure is always at 50 PSI constant, even if you are in the shower for a month. and the heater keeps working.

 

[LCF]

Thanks Valveman. I was going to ask if a cycle stop valve would be a cheaper fix for my pressure tank issues. Right now there is a shortage on pressure tanks and the prices seem higher than when I last bought one two years ago. It would certainly be easier and more cost effective for me to use a cycle stop valve instead. I will probably buy a valve and replace the tank with a much much smaller one later on. Hopefully I will have a perfect shower very soon!

 

[Bannerman]

will probably buy a valve and replace the tank with a much much smaller one later on.

If you obtain the PK1A kit, that includes the CSV, pressure tank, pressure switch and wall bracket.

The entire project can then be easily completed in one go.

https://cyclestopvalves.com/