Hotwater heater

[Wlafleur]

I have a keystone passport and anytime my hot water heater kicks on my hot water line under the sink leaks. The line does not leak when the hot water heater is off and I run water through it. What is causing this and what can I do to fix it?

[chuckster57]

Welcome to the forum

I would check the hot supply line where it connects to the faucet. There is a seal there and they can fail, or the fitting comes loose. If the seal has failed, any big box hardware store should have them, called a 1/2” swivel seal.

[bobbecky]

The water systems on RV’s are a closed system. There is a check valve where your city water hose connects so water doesn’t leak backwards. When the water heater comes on, the pressure in your plumbing increases due to the water expanding when heated. If you have any weak connection, this will be the time it will leak. It is also why the pressure relief valve on the water heater will leak when the water heater is heating if you don’t have an air pocket in the water heater tank.

[skids]

Originally Posted by bobbecky

The water systems on RV’s are a closed system. There is a check valve where your city water hose connects so water doesn’t leak backwards. When the water heater comes on, the pressure in your plumbing increases due to the water expanding when heated. If you have any weak connection, this will be the time it will leak. It is also why the pressure relief valve on the water heater will leak when the water heater is heating if you don’t have an air pocket in the water heater tank.

I believe that heated water does not appreciably expand until it reaches the boiling temperature - which it is NOT supposed to do. The air pocket above the water in the tank does increase pressure as temperature rises from cold to hot. Once you turn on the hot faucet it should again reduce pressure and reach an equilibrium pressure.

[bobbecky]

The instant you begin adding heat to water, it begins to expand. It doesn't suddenly expand at a certain temperature.

[skids]

I agree Bobbecky - sort of. Since the volume of air in the tank is constant, the pressure rises with temperature. Water does not expand by simply increasing temperature. It weighs one gram cubic cm from 33 F to the boiling point. In other words, no appreciable expansion. The air above the water is what increases pressure on the hot water.

[flybouy]

What hasn't been mentioned is the change in viscosity with temperature. When water is heated it's less viscose then when cold.

[Balvar24]

Originally Posted by flybouy

What hasn't been mentioned is the change in viscosity with temperature. When water is heated it's less viscose then when cold.

Most fluid viscosities change with temperature. Both Dynamic and kinematic viscosities.

Water, for the most part behaves as Newtonian. Where it get's nuts is with non-newtonian fluids. Like ketchup. It's shear thinning. The faster it moves, the less viscous it is at a constant temperature.

[JRTJH]

All these "high tech conditions and physics explanations" for a LOW TECH problem.....

He's got a dripping connector fitting under the kitchen sink that only drips once, then works OK. Chances are very, VERY good that it's the foam cone washer in the fitting that's either not tight enough (needs tightening) or is too tight and deformed (needs replaced and properly tightened)....

As for the amount of air expansion vs water expansion and the temperatures and pressures at which they affect a "drip under the sink 15' away" .... Well, way too "high tech" for a Keystone trailer water plumbing system.....

[wiredgeorge]

Originally Posted by JRTJH

All these "high tech conditions and physics explanations" for a LOW TECH problem.....

He's got a dripping connector fitting under the kitchen sink that only drips once, then works OK. Chances are very, VERY good that it's the foam cone washer in the fitting that's either not tight enough (needs tightening) or is too tight and deformed (needs replaced and properly tightened)....

As for the amount of air expansion vs water expansion and the temperatures and pressures at which they affect a "drip under the sink 15' away" .... Well, way too "high tech" for a Keystone trailer water plumbing system.....

I had to replace one of those cone washers last year. I have found that if it leaks and is "retightened" if will deform and leak even more. See these threads:
https://www.keystoneforums.com/forum...highlight=cone
https://www.keystoneforums.com/forum...t=kitchen+leak

[chuckster57]

Originally Posted by wiredgeorge

I had to replace one of those cone washers last year. I have found that if it leaks and is "retightened" if will deform and leak even more. See these threads:
https://www.keystoneforums.com/forum...highlight=cone
https://www.keystoneforums.com/forum...t=kitchen+leak

I have found it depends on the age and how tight the fitting was in the first place. Over the years, I’m over 90% success rate with tightening, trick is to not overtighten.

[sourdough]

Originally Posted by wiredgeorge

I had to replace one of those cone washers last year. I have found that if it leaks and is "retightened" if will deform and leak even more. See these threads:
https://www.keystoneforums.com/forum...highlight=cone
https://www.keystoneforums.com/forum...t=kitchen+leak

Those cone washers are handy until they aren't. One of my routines is to go through water connections after I purchase a trailer and cinch all of them down. Same went for my toilet connection on this trailer. On my first trip it started dripping so I opened it up and found the cone washer a little crimped sideways. Straightened (I thought) and cinched it down some more. Started leaking again but it was then so tight I would have needed pliers to tighten it more. Pulled it back apart and that cone washer had somehow misaligned itself when I reinstalled it. Replaced it and hand tight fixed the leak. Ultimately I just cut the pex off, installed a shark bite fitting and put a 1/4 turn cutoff and residential toilet hose on the toilet - happy camper since.

[dutchmensport]

OK, I know I retired only 2 weeks ago and already my mind has slipped into la-la land, and because of my age, I guess I'm entitled to not have to "think" any more, so maybe it's just me. But I missed the pun above?

(I told my wife that if I ever got stopped by law enforcement for a traffic violation, I'll respond to the officer: Officer: What your name there fellow? Me: Well sir, I'm sorry, if you don't know I can't help you. I don't remember it either!" Retirement! A good excuse to forget everything