T&P valve drips only on propane?

[rbTN]

so I noticed the other day a drip coming from the bottom of the water heater panel, opened it and the t&p valve had a slow drip. Tried opening and closing it several times but it didn't really improve so ordered a new one.

I've not received the new valve yet but pulled into a site with fhu so switched to elec on the water heater... no drips. Ok, used propane the next time I needed hot water just to confirm and it starts dripping again!

The flame looks and sounds good and it cycles fine, just the valve drips using propane. Its the original valve from 2006 so I will replace it but wonder if they become more sensitive to temp as they age? I would think just the opposite.

[rbTN]

I should have searched first before posting - I found this on A RV repair site


"Dripping pressure relief valve. This happens when the air pocket at the top of the water tank is absorbed by the water. The are pocket normally allows for the expansion of the water as it is heated. When there is no air pocket the water and pressure is released through the pressure relief valve."

I'm guessing that the propane generates more heat so causing a more rapid expansion. I'll try this later today and see if it helps.

[jacwjames]

You might try opening the relief valve and flush it out good. A small piece of dirt/debris could cause it to leak. It continues you may have to replace.

[bddadles]

I would start by turning off the power to the heater and then drain and flush the tank. Refill and then turn the power back on. If it still leaks replace the valve. I agree that the gas side probably heats hotter than the electric. If it still happens I would check into replacing the thermostat for the gas side. If it is a suburban it is easy. I don't know about an Atwood.

[Old-Biscuit]

It appears that Denali uses an Atwood Brand Water Heater


Yours being a 2006 year then that Atwood uses SAME set of T-stats for BOTH electric and gas heat functions....so both heat sources would heat water to SAME temp (140*F/T-stat) and if it fails to Open then the ECO (Energy Cut Off/Hi Temp Tstat) would Open at 180*F/trigger FAULT Light /lockout water heater functions until manually reset.


Gas DOES recover heat faster then electric
Electric...roughly 6 gal/hr from initial fill temp
Gas....roughly 10 gal/hr from initiial fill temp



Water swells when heated......increase in volume causes increase in pressure inside the WH tank
Air can be compressed.........air pocket helps to control pressure increases from water swelling
Water can NOT be compressed.......so lack of air pocket pressure WILL increase
Gas transfer heat quicker then electric so water will swell faster which can cause rapid increase in pressure in WH Tank


2006 T&P Relief Valve most likely has scale/calcium built up on valve seat/stem and the spring has probably weaked from thermal stresses.
New T&P is good idea. Standard 3/4" NPT with short probe (any hardware store so hopefully you didn't over pay for an 'RV' T&P)


Couple wraps of Teflon Tape

After installing let it SNAP close
THEN turn water supply on and bleed air from hot side via closest faucet NOT via the new T&P
After WH Tank is filled and air bled from hotside then turn on GAS and heat water.
Check if T&P weeps (IT SHOULDN'T)

[Old-Biscuit]

Originally Posted by bddadles

I would start by turning off the power to the heater and then drain and flush the tank. Refill and then turn the power back on. If it still leaks replace the valve. I agree that the gas side probably heats hotter than the electric. If it still happens I would check into replacing the thermostat for the gas side. If it is a suburban it is easy. I don't know about an Atwood.

Doesn't your 2008 NUWA have an Atwood?

[rbTN]

tried creating an air pocket yesterday afternoon but it didn't help so I'll replace it as soon as the one I ordered comes in and report back after

thanks everyone

[bddadles]

Originally Posted by Old-Biscuit

Doesn't your 2008 NUWA have an Atwood?

No. 10 gal. Suburban.

[Ljwt330]

Originally Posted by bddadles

No. 10 gal. Suburban.

There is a slight difference in a Surburban from what Old-Biscuit posted in that yours has two separate thermostats. This does raise the possibility that the gas thermostat is heating beyond it factory setting, but not high enough to trip the ECO. Conversely, the electric thermostat may not be heating high enough and a weak T&P is not weeping because the water is not hot enough.


Regardless, change the T&P and if that solves the issue, your good. You may wish to check the water temp, when each system is heating the water independently, just to see if there is a variation in hot water when using gas vs electric. On my Surban I noticed a distinct temperature differential between heating on electric that was noticeably lower than on gas. I replaced the electric thermostat and now both systems heat the water to the same temperature.

[Old-Biscuit]

Originally Posted by Ljwt330

There is a slight difference in a Surburban from what Old-Biscuit posted in that yours has two separate thermostats. This does raise the possibility that the gas thermostat is heating beyond it factory setting, but not high enough to trip the ECO. Conversely, the electric thermostat may not be heating high enough and a weak T&P is not weeping because the water is not hot enough.


Regardless, change the T&P and if that solves the issue, your good. You may wish to check the water temp, when each system is heating the water independently, just to see if there is a variation in hot water when using gas vs electric. On my Surban I noticed a distinct temperature differential between heating on electric that was noticeably lower than on gas. I replaced the electric thermostat and now both systems heat the water to the same temperature.

bddadles wasn't having temp issues with his Water Heater.
He mentioned he didn't know about Atwoods and I questioned whether he had an Atwood on his 2008 NUWA


Mine uses an Atwood....thought NUWA used them across their line of RVs.


OP has an Atwood and it only uses one set ot t-stats for both electric/gas heating control

[Ljwt330]

Originally Posted by Old-Biscuit

bddadles wasn't having temp issues with his Water Heater.
He mentioned he didn't know about Atwoods and I questioned whether he had an Atwood on his 2008 NUWA


Mine uses an Atwood....thought NUWA used them across their line of RVs.


OP has an Atwood and it only uses one set ot t-stats for both electric/gas heating control

LOL, that's what I get for not remembering the screen name of the OP after reading through the posts.

[Old-Biscuit]

Originally Posted by Ljwt330

LOL, that's what I get for not remembering the screen name of the OP after reading through the posts.

I get side tracked on EVERY thread.......

[rbTN]

update - no improvement at this point

I replaced the old valve, still dripped, have attempted to create the air pocket multiple times to no avail

I have determined it is not related only to propane as I initially thought, it happens on electric as well, just take a little longer to start.

It has to be related to the air pocket. After multiple uses I have found that it is only on the initial heating of the water each day. If it is dripping I can open the faucet and let off the excess pressure and it will be fine after that no matter how long I leave it on and use hot water.

To create the air pocket I have turned off the water, let off all pressure, opened the T&P valve till it stops, close T&P, turn on pump, bleed air from the lines at faucet, turn on heat.

The one thing I have not tried is to let water out of the drain with the T&P open, then close the T&P, then close the drain to see if I can make a larger air pocket. I may try that later today

[l1v3fr33ord1]

rbTN-

You probably found this in the Atwood documentation, but for the sake of others who may not know it, here is the procedure to establish an air pocket:

1. Turn off water heater.
2. Turn off incoming water supply.
3. Open the closest hot water faucet in the coach.
4. Pull handle of pressure-temperature relief valve straight out and allow water to flow until it stops.
5. Allow pressure-temperature relief valve to snap shut, close the faucet then turn on the water supply.

Atwood also says this in the installation/owner's manual

When pressure-temperature relief valve discharges again, repeat above procedure. For a permanent solution, we recommend one of the following:

• Install a pressure relief valve in cold water inlet line to water heater and attach a drain line from valve to outside of coach. Set to relieve at 100-125 PSI.

• Install a diaphragm-type expansion tank in cold water inlet line. Tank should be sized to allow for expansion of approximately 15 oz. of water and pre-charged to a pressure equal to water supply pressure.

These devices can be obtained from a plumbing contractor or service center.

Our coach's water heater could not maintain an air pocket. I followed the second Atwood recommendation, and it fixed the problem. If you would like details, send me a private message.

Note: If the P-T relief valve leaks due to pressure it means the pressure in the water heater is around 150 psi. Depending on the way the heater is plumbed, some parts of the water system in the RV may see the same pressure as in the water heater- and 150 psi is much higher than recommended for RVs. As you can see, the air pocket is very important.

By the way, the weeping will occur several times a day, if you allow the water in the water heater to get cold. It's the expansion from cold to hot (approx. 140 deg. F) that creates the pressure to lift the P-T relief valve. The water heater insulation keeps the water inside warm enough that the weeping doesn't occur again over the course of a few hours.