WH T&P valve drips on electric but not gas

Lynnmor wrote:
If the heating element is cracked open, exposing the internal parts to water, it will cause gas to form. Does the dripping stop as soon as you open a hot water faucet? If it does, then the pressure is increasing while the water is turned off. Does the heater make a louder than usual hiss sound when the heating element is operating? You might want to pull the element and have a look.

Never heard of an electric element gassing :H

Where do you get this information?

Have heard them hiss.....typically from being scaled up.

If the heating element is cracked open, exposing the internal parts to water, it will cause gas to form. Does the dripping stop as soon as you open a hot water faucet? If it does, then the pressure is increasing while the water is turned off. Does the heater make a louder than usual hiss sound when the heating element is operating? You might want to pull the element and have a look.

Snowman9000 wrote:
No, there is no mixing valve.

I don't know why it would be losing the air pocket, but I guess it could. Seems like it would do the same on gas or electric, but obviously the electric is running hotter.

Our trip is ending tomorrow and we'll be back in the cold weather. So I'll mess with it when spring sets in. Thanks for the tips.

Loss of air pocket happens...air gets absorbed into water, air gets bled off during usage etc. It happens.

Is it an Atwood or a Suburban?

IF Atwood....is it older than 2004 model?
Prior to 2004 Atwood used separate t-stats for electric & propane.

If Suburban...they use separate t-stats for electric & propane.

So if separate t-stats.then electric could be slightly overheating on electric

No, there is no mixing valve.

I don't know why it would be losing the air pocket, but I guess it could. Seems like it would do the same on gas or electric, but obviously the electric is running hotter.

Our trip is ending tomorrow and we'll be back in the cold weather. So I'll mess with it when spring sets in. Thanks for the tips.

IF t-stat is not tight against WH Tank wall it can cause overheating BUT if normal t-stat opens 'late' then it is still working unless High Temp t-stat opens. When Hi temp t-stat opens you will get a fault light and WH will not reheat until reset. So you would know if high temp t-stat opened.

Suburban WH use a 120V AC set of t-stats for electric and they use a 12V DC set of t-stats for propane.

Both sets of t-stats are pre-set snap discs----Normal is 130*F and High temp is 170*F. For BOTH electric & propane t-stats.
The T&P valve is set to open at 210*F and/or 150# pressure.

Atwood WH use one 12V DC set of t-stats for both electric & propane.
Normal set for 140*F and ECO (Hi Temp) set for 180*F.
T&P same as Suburban...210*F and 150#

Atwood has the XT WH that uses the mixing valve. Same t-stats for electric & propane but normal set for 160*F.......then mixing valve is set for 130*F output. Same Hi temp and T&P settings.

WEEPING of T&P is common when heating water in a closed system (such as RV plumbing system is) because water expands when it is heated.

A 'air pocket' by design is at top of WH Tank. It allows for the expansion of water when heated without the increase in pressure. (air can be compressed...water doesn't)

If air pocket is lost or marginal the increase in pressure is enough to cause T&P to weep.
Normal in a closed system. Not unheard of. Doesn't mean T&P is faulty.

You can re-establish air pocket
Turn water supply off
Open faucet hotside to relieve pressure
Open T&P via lever.......when water stops running out of T*P left it snap close
Close faucet
Turn on water supply

Weeping can occur with either Atwood or Suburban. Both reference issue in their manuals.

Air Pocket is by design

Hi,

Probably should check the temperature of the hot water after it has had a little while to heat up on electric.

If it is over 165F, then the pressure relief is letting out water because it is tow warm. You also risk scalding. Does your RV have a water mixing valve on the outlet of the water heater? Some are now using super hot water and a mixing valve to lower the temp to around 120F, so you would be mixing 160F water from the heater with cold water at around 60% hot and 40% cold, to get 120F output. This means that about 10 gallons of 120F water is made with 6 gallons of 160F water and 4 gallons of water from the fresh water tank.

Yes the thermostat is something to look at.

Also is the water pump on at the same time? Perhaps the water line pressure was at 60PSI when the pump stops, and you warm 65F water to 140F. This can increase the pressure in the hot water lines (there is a check valve) and opening the hot water line can release this increased pressure, as well as stop the dripping (I hope).

I was watching a TV show, and they explained that the incoming water pressure to the house was 150 PSI from the street, and there is a pressure reduction valve, much like a RV has to have only 60 PSI in the home. There is a check valve in the water heater inlet, so it will not backflow hot water into the cold water lines. What the family reported to 'This old House' was that they filled a 5 gallon bucket each week, and had to dump it weekly. The solution was a hot water rated pressure tank, and reducing the incoming water pressure to only 50 PSI. Now when nobody is using the hot water, and the tank heats from 75F to 130F, the pressure barely goes above 60 PSI, because the water is moving into the expansion tank.

Before adjusting the pressure reduction valve, and installing the expansion tank, the water pressure measured in the hose bib at the bottom of the hot water tank would increase from 70 PSI with cold water to 150 PSI with hot water, when the pressure relief valve would start to seep out some water. So the pressure relief valve was doing it's job, reliving all water pressure over 150 PSI.

Fred.

Yeah, that's about how I see it. And it's dripping fairly fast, probably 1x/second. Seems like the thermostat might be the problem. Is there one for the electric side and a different one controlling the gas?

Could be the water in the heater is heating up just to the point of popping the valve, but not quite, but just a bit allowing it to drip.The electric is getting the water hotter than the gas. If this is happening, not much you can do about the relief valve, it's doing it's job.

If it is just a slight drip, I wouldn't worry about it. Mine drips sometimes, enough to leave a little puddle of water in the bottom of outside cabinet area. But, I've never seen it actually drip. So I figure the heat in the heater is at that point, and the valve is doing it's job. I don't worry about that little puddle of water.

Now, if your valve is dripping fast, like 1 drop a second, or faster, then something is definitely getting too hot. Considering this is your second valve, I'd say there's nothing wrong with the relief valve. It's working as it's suppose to. The problem is elsewhere. (getting too hot).