water heater problem

[Norm Mayer]

I just replaced a leaking water heater and ran into a strange problem. Now, when taking a shower the water keeps cycling from cold to scalding, without touching the valves. It didn't happen till I installed the new water heater! Any ideas what could be wrong?

 

[Brian Degulis]

Is it possible you mixed up the in and out water conections on the heater?


Brian

 

[MikeP]

Sounds as if the pressure tank has either failed (ruptured bladder) or has the incorrect amount of air pressure. The symptom you describe is typical of that.

Drain all pressure from the system by turning off the pump and turning on a hot and cold faucet until no water runs out. Your pressure tank should have a valve that looks just like the valve on your car tire for adding air.

Check the pressure at that valve. It should be 2PSI below the cut off pressure of the pump. In other words, if the pump cut off is set at 30PSI, the air pressure in the tank should be set to 28PSI. This check is just an "information" check for now. Release all the pressure from the tank and note if any water comes out of the valve. If it does, the tank needs to be replaced.

If no water comes out, repressurize the tank to the 2PSI below pump cutoff pressure.

Note that if you use shore water connections when at the dock, the input pressure (after the regulator) and the water pump's pressure setting should be set the same for the pressure tank to function equally well with shore or internal water.

 

[Norm Mayer]

To further clarify, I am running off the tank, not shore water. When the water pump is running, the water is cool; when the pump shuts off, that is when the water gets very hot. I checked to see if there is water in the surge tank and there was'nt. I also repressurized the tank, but now the pump cycles too much. I may try letting a few pounds of pressure out. Thanks for the help!

 

[REBrueckner]

The output from your water pressure pump should go to the pressure/surge tank first, from there in parallel to both your water heater and cold water supply keeping pressure in both hot and cold legs to faucets equal.

Is your problem now corrected?? A kinked hose??

 

[Finalee]

Is the problem isolated to the shower? Debris may have lodged in the shower equalizer causing the problem. It may also get in the other faucets.

 

[Brian Degulis]

To further clarify, I am running off the tank, not shore water. When the water pump is running, the water is cool; when the pump shuts off, that is when the water gets very hot. I checked to see if there is water in the surge tank and there was'nt. I also repressurized the tank, but now the pump cycles too much. I may try letting a few pounds of pressure out. Thanks for the help!

New water heaters have a restrictor in them. It's usually a plastic insert in the input and output lines. Considering that they are intended for use with city water where the pressure is constant and higher these restrictors may be causing your problem. When your pump turns off pressure is highest so water is going thru the heater. When pressure drops (pump running) not enough water goes thru the heater. If you have these on your new heater you might try taking them out? Or first try shore water and see if there is any change.

Brian

 

[Trojan]

If your explanation is correct. You could have a bad mixer valve on your faucet. The pressure tank has nothing to do with the water flow to the shower or the pump pressure. It feeds both hot and cold lines with the same pressure. The only thing that controls the mix is the mixer valve on the shower it's self. Even hooking the tank up backwards will not cause the problem you are having. Hooked back wards You could run out of hot water, but that all depends on the size of the tank. Cold is fed to the bottom of the tank and the hot is taken off the top. If there is no other water drain on the cold supply side after the hot and cold split. The water supply to the shower should be constant. There is the slight chance that you have an under sized cold water feed after the split to the mixer valve. That could cause this, but it would only happen with an extreme water pressure change. You did not say what pressure range you were running. But you did say it happens when the pump is off. Take apart the mixer valve and check it. If it's OK then check the cold water supply line for a restriction after the split. If the flow rate at the mixer is small. The pressure out will remain constant. If the flow rate is large and the flow to the cold feed is restricted. You will have more hot than cold and if the pressure varies a lot. You could have great temp swings depending on the restriction size when the pump is on or off.

BILL

 

[MikeP]

A faulty pressure tank WILL cause hot/cold variations as you shower. I ran into this when I replaced the tank a few years ago. I couldn't figure out what was going on until a plumber who was familiar with this told me to check out the tank and pressure. It solved the problem when I adjusted the Pressure tank to the proper pressure...

Certainly I'm not saying that this is the only possible cause BUT it sure CAN cause this problem.

 

[Trojan]

A faulty pressure tank WILL cause hot/cold variations as you shower. I ran into this when I replaced the tank a few years ago. I couldn't figure out what was going on until a plumber who was familiar with this told me to check out the tank and pressure. It solved the problem when I adjusted the Pressure tank to the proper pressure...

Certainly I'm not saying that this is the only possible cause BUT it sure CAN cause this problem.

Your correct.
But, I don't think that you were having the extreme changes in temp that he says he is having. You could have the same trouble if the pump pressures were set incorrect. Real high and real low. There is always some restriction in the valve in order to change the mix. It could be all pressure related. He never said what pressure he was running. I don't think we have all of the picture. He said All he did was change the hot water tank.

BILL

 

[Norm Mayer]

I don't know what water pressure I am running, but per previous suggestions I released all pressure in the surge tank and got no water. I then applied 38 psi pressure to the tank, but the pump started running the instant the water was turned on. I released some pressure on the tank, and that problem was solved, as well as the worst of the temperature swing. But some swing is still evident. I also suspect the pressure switch on the pump is set too high, as it labors, almost to the point of stalling, as it nears shutoff. The strange part in all this is originally, only the water heater was changed and then the other problems developed. The boat is out of the water for new bottom paint, so it will be a while before we can see how bad the water temp variation really is. By the way, the temp swing is at ALL faucets, not just the shower.