(Solved) Water heater pressurizing the system over the regulated pressure when heating from cold to hot

[marknewbill]

Hi,
(Hot water heater seems to pressurize my system to a high level)
I did some searching and did not find this exact question.

for the specifics, I am using a 40psi regulator, and I pressure tested it to see that it is functioning properly and not leaking in high pressure water. so that is not the issue.
I also did not do anything to purposely bleed the air out of the top of the heater, I just connected the water and bled the air from the kitchen sink until the bubbles stopped. Otherwise the heater seems normal and I get about the normal amount of hot water out of it.

The issue: I have noticed the water pressure in my camper is really high when you first open the valves after the water heater has finished running after completely using all the hot water, and then finishes heating the full tank again. I don't believe it is making steam, as the water doesn't seem that hot and it does it on electric and propane (assuming here the control for the temperature is separate for electric or propane, it may not be however.). I do need to measure it somehow to see, but it really just seems about 130 degrees or so.
I am a new owner and no experience, here is what I find though - since the system is closed by a check valve on the incoming water, as the water heater heats a full load of cold water to the full temperature - either on propane or electric the pressure in the camper gets "super pressurized" from the expansion of the water and air blanket in the heater.

I don't know what the pressure is, but if I estimate, it is probably 80 psi since it comes out with twice the normal force for a couple seconds the first time you open the valve on a sink after the heater has shut down from a cold start. It will then be normal each opening of the valve until I use up all the hot water and wait for reheating, high pressure presents itself again upon the next valve opening.

I know one of those expansion tanks will solve that issue, but this is a brand new camper, should I be concerned about damaging the plumbing by this high pressure?

This is on our brand new RE275 Pioneer.

Thanks,
MN

 

[centerline]

Re: Water heater pressurizing the system over the regulated pressure when heating from cold to hot

Hi,
(Hot water heater seems to pressurize my system to a high level)
I did some searching and did not find this exact question.

for the specifics, I am using a 40psi regulator, and I pressure tested it to see that it is functioning properly and not leaking in high pressure water. so that is not the issue.
I also did not do anything to purposely bleed the air out of the top of the heater, I just connected the water and bled the air from the kitchen sink until the bubbles stopped. Otherwise the heater seems normal and I get about the normal amount of hot water out of it.

The issue: I have noticed the water pressure in my camper is really high when you first open the valves after the water heater has finished running after completely using all the hot water, and then finishes heating the full tank again. I don't believe it is making steam, as the water doesn't seem that hot and it does it on electric and propane (assuming here the control for the temperature is separate for electric or propane, it may not be however.). I do need to measure it somehow to see, but it really just seems about 130 degrees or so.
I am a new owner and no experience, here is what I find though - since the system is closed by a check valve on the incoming water, as the water heater heats a full load of cold water to the full temperature - either on propane or electric the pressure in the camper gets "super pressurized" from the expansion of the water and air blanket in the heater.

I don't know what the pressure is, but if I estimate, it is probably 80 psi since it comes out with twice the normal force for a couple seconds the first time you open the valve on a sink after the heater has shut down from a cold start. It will then be normal each opening of the valve until I use up all the hot water and wait for reheating, high pressure presents itself again upon the next valve opening.

I know one of those expansion tanks will solve that issue, but this is a brand new camper, should I be concerned about damaging the plumbing by this high pressure?

This is on our brand new RE275 Pioneer.

Thanks,
MN

you really need to put a gauge on the water line.... 130 is plenty warm for the water, as they are usually set to heat to about 120 degrees...

as far as the pressure goes, you definitely arent getting 80psi built up in the system or you would have leaks and possibly a ruptured line, but it is true that if there is air in the tank that is being heated, the pressure will climb higher than normal, but if the water was being heated enough to cause the water to turn to steam in the system, you would be in danger of a boiler explosion or line rupture, but there is a over-pressure pop-off valve on the water heater tank to prevent this... if its not dumping water out the pop-off valve periodically, the pressure in the tank isnt at a dangerous level

most systems will have a higher standing pressure than the working pressure, which is due to the pump building pressure to its limit and then shutting off.... when the faucet is turned on, this pressure escapes and the pump activates again, BUT, if it builds to its maximum again, it will shut off again, and so with the faucet open, it wont build to the same pressure that it was when you first opened the faucet....

sometimes the water flows out of the faucet slowly, due to a small line, a pinched line, or the faucet being turn on just a little, in which case you will see to pressure build and drop as it flows, due to the pump cycling, running to built pressure and then shutting off til the pressure drops, which then causes the pump to turn on again....

some systems have more piping than others, and some are equipped with an accumulator to help balance the water pressure, and this can affect how long the system seemingly holds its pressure in the system, but the standing pressure will be determined by the pump setting, and the flow rate will be determined by pump size AND water line size....

 

[danemayer]

Re: Water heater pressurizing the system over the regulated pressure when heating from cold to hot

Hi marknewbill,

I think you have it pretty much figured out. In a closed system, the heat causes expansion of the water, causing what you've been experiencing. Suburban says pressure can build to 150 psi before the temperature/pressure relief valve allows water to seep out. To reduce this, they suggest creating the air pocket. Watch out for your hand when opening the relief valve.

1. Turn off water heater.
2. Turn off cold water supply line.
3. Open a faucet in the RV.
4. Pull out on the handle of the Pressure Relief (P & T) Valve and allow water to
flow from the valve until it stops.
5. Release handle on P & T Valve - it should snap closed.
6. Close faucet and turn on cold water supply; as the tank fills, the air pocket
will develop.

 

[marknewbill]

Re: Water heater pressurizing the system over the regulated pressure when heating from cold to hot

you really need to put a gauge on the water line.... 130 is plenty warm for the water, as they are usually set to heat to about 120 degrees...

as far as the pressure goes, you definitely arent getting 80psi built up in the system or you would have leaks and possibly a ruptured line, but it is true that if there is air in the tank that is being heated, the pressure will climb higher than normal, but if the water was being heated enough to cause the water to turn to steam in the system, you would be in danger of a boiler explosion or line rupture, but there is a over-pressure pop-off valve on the water heater tank to prevent this... if its not dumping water out the pop-off valve periodically, the pressure in the tank isnt at a dangerous level

most systems will have a higher standing pressure than the working pressure, which is due to the pump building pressure to its limit and then shutting off.... when the faucet is turned on, this pressure escapes and the pump activates again, BUT, if it builds to its maximum again, it will shut off again, and so with the faucet open, it wont build to the same pressure that it was when you first opened the faucet....

sometimes the water flows out of the faucet slowly, due to a small line, a pinched line, or the faucet being turn on just a little, in which case you will see to pressure build and drop as it flows, due to the pump cycling, running to built pressure and then shutting off til the pressure drops, which then causes the pump to turn on again....

some systems have more piping than others, and some are equipped with an accumulator to help balance the water pressure, and this can affect how long the system seemingly holds its pressure in the system, but the standing pressure will be determined by the pump setting, and the flow rate will be determined by pump size AND water line size....

Hello !
Thanks for the response. For clarity, I do have some leaks, a lot of the thumb wheel nuts were leaking on faucet and toilet and water heater connections in 3 areas. I tightened these more by hand and believe the leaks have stopped. I was only using city water at the time with a 40psi regulator, the pump was not on. maybe it is not 80 PSI but certainly noticeably more than 40 when this occurs.

I will need to check the water temp when I un-winterize next time and see where it is. Getting a pressure gauge will be more of a challenge, as I currently don't own a water pressure gauge that can connect to a faucet, and one on the outside regulator wont help since there is a check valve between it and where the pressure seems to be.

- - - Updated - - -

Hi marknewbill,

I think you have it pretty much figured out. In a closed system, the heat causes expansion of the water, causing what you've been experiencing. Suburban says pressure can build to 150 psi before the temperature/pressure relief valve allows water to seep out. To reduce this, they suggest creating the air pocket. Watch out for your hand when opening the relief valve.

1. Turn off water heater.
2. Turn off cold water supply line.
3. Open a faucet in the RV.
4. Pull out on the handle of the Pressure Relief (P & T) Valve and allow water to
flow from the valve until it stops.
5. Release handle on P & T Valve - it should snap closed.
6. Close faucet and turn on cold water supply; as the tank fills, the air pocket
will develop.

Thanks, I will review this again when I fill the next time. one of my proposed modifications when the warranty is out is to add some sort of pressure reservoir like a small well has that will help even out the pumping situation and this as well. Im thinking to do a good job it probably needs to be about 5 gallons, and then where in the world will I hide that. anyway, thanks and I will check the water temp next run and see where it is. maybe it is just a little high. do they have adjustments like the home water heaters do?

this one is a new dometic unit for gas and electric I believe.

Thanks again!

 

[centerline]

Re: Water heater pressurizing the system over the regulated pressure when heating from cold to hot

one of my proposed modifications is to add some sort of pressure reservoir like a small well has that will help even out the pumping situation.... Im thinking to do a good job it probably needs to be about 5 gallons.

I will check the water temp next run. do they have adjustments like the home water heaters do?

Thanks again!

a Well?... thats basically what you have right now... you have a bulk of water sitting below, and a pump that brings it up under pressure, for use.

you need to look at accumulators, also known as pressure tanks... a 5 gallon is overkill, as most accumulators for RVs and boats are about a pint or a quart size, and fully adequate... 1 to 2 gallon pressure tanks are used in reverse osmosis systems that are designed for rv/boat use...

but if the water heater is causing the high pressure in the system, its a good option, as it will allow for a smoother transition in the water flow/pressure drop, when the faucet is opened...

CAUTION, some of the more advanced RV water pumps dont work well with an accumulator tank.... if its a "variable flow" pump, an accumulator is not really a reasonable option, but accumulators work great with the standard water pumps..

generally, the water heaters have a fixed thermostat, but for about $20, you can purchase an adjustable thermostat for the water heater that is easily installed yourself in about 10 minutes, and they work great.

 

[TedS]

Re: Water heater pressurizing the system over the regulated pressure when heating from cold to hot

Get an rv accumulator.
https://www.amazon.com/s?k=rv+accum...11119121&tag=hydsma-20&ref=pd_sl_2d5jhzw48u_e

Water will expand about 1 cup for a 6 gallon water heater going from cold to hot.

 

[marknewbill]

Re: Water heater pressurizing the system over the regulated pressure when heating from cold to hot

Get an rv accumulator.
https://www.amazon.com/s?k=rv+accum...11119121&tag=hydsma-20&ref=pd_sl_2d5jhzw48u_e

Water will expand about 1 cup for a 6 gallon water heater going from cold to hot.

Thanks, I will look into that. I believe what happened to me is I put in the water before leaving home to have it hot when I arrived and maybe the air blanket sloshed out into the lines on the way. that could explain why i found this issue on the first day out. No doubt this would solve that problem.

 

[marknewbill]

Re: Water heater pressurizing the system over the regulated pressure when heating from cold to hot

update:

found out that what happens is when driving the water in the heater moves around and the air pocket gets dispersed in the lines. so now when I arrive, first thing I do is drain some water from the heater until it is below the temp valve and then fill the tank and turn it on. doing this I have had no more overpressure issues. same as the burp technique, except I now practice it at every stop. I am sure the accumulator will also solve it where this step is not required. I will probably add that when the warranty runs out.