Hotwater heater

Wlafleur · 01-19-2022, 09:58 AM

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** · 01-19-2022, 10:12 AM

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 · 01-19-2022, 10:20 AM

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 · 01-19-2022, 06:02 PM

Quote:

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 · 01-21-2022, 02:08 PM

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

skids · 01-21-2022, 02:32 PM

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.

Balvar24 · 01-25-2022, 03:02 PM

If you look at the water heater instructions, it tells you how to keep a pocket of air in the water heater to offset thermal expansion and resulting over pressure of the hot water system. This could be a portion of or your entire problem.

Water is relatively in-compressible, while air is relatively compressible (think air in the brake lines). The water heater air pocket works like the old hydronic heating air compression tanks in buildings that were more common before the bladder and membrane tanks came out that are more commonly in use now.

Water gets hot and expands into the air pocket. For every degree warmer water gets, it expands more. Pressure rises but very little until the air pocket reaches the point where it is no longer relatively incompressible. Technically speaking, air is only MORE compressible than water. The quantity of air never changes, but the volume it occupies changes as the water expands.

When you size an expansion tank, you must first calculate the volume of water in the system. Then you have to calculate the amount of expansion based on temperature rise from cold to hot. Locally, in a home it's 50F to 140F (or there-abouts). I don't know what temperatures the RV equipment manufacturers use. Then, you select based on (1) initial pressure and (2) maximum allowable working pressure, the required acceptance volume and total volume required because you always have to have some volume in the system for the constant amount of air to occupy.

1. Check that you've filled the water heater per the instructions.

2. Is the relief valve opening?

3. If 1 and 2 above are good, check the faucet connection. They're often "quick connects" and the ones most likely to leak. You could be missing a gasket.

**flybouy** · 01-25-2022, 04:01 PM

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

Balvar24 · 01-25-2022, 05:27 PM

Quote:

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** · 01-25-2022, 06:01 PM

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 · 01-26-2022, 04:24 AM

Quote:

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** · 01-26-2022, 04:37 AM

Quote:

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.

wiredgeorge · 01-26-2022, 04:44 AM

Quote:

Originally Posted by chuckster57

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.

We have a 20 year old trailer and when tightening the dripping fittings found they were badly deformed and new was the only answer. I use finger tight on those fittings. Just tossing this out as a possible fix for the OP's leak. I would should try tightening first but if it still leaks, new washers would likely fix the problem.

I don't do this stuff for a living and my experience extends to my one case of the drip (so to speak).

**chuckster57** · 01-26-2022, 04:46 AM

Yup! I suggested the OP try tightening a bit, and replacing if needed, only reason I posted my success rate is I have done a couple more than some

skids · 01-26-2022, 07:11 AM

Quote:

Originally Posted by chuckster57

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.

This is what I like: Practical information and solutions.

**sourdough** · 01-26-2022, 07:50 AM

Quote:

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.

jimborokz · 01-31-2022, 06:49 AM

A very interesting thread. I'm still looking to get ketchup from my faucet.
However one thing y'all did do was bring to mind that I need to restore the air cushion in my HW tank as I've noticed the relief valve dripping a lot.

Balvar24 · 02-01-2022, 12:02 PM

Quote:

Originally Posted by jimborokz

A very interesting thread. I'm still looking to get ketchup from my faucet.
However one thing y'all did do was bring to mind that I need to restore the air cushion in my HW tank as I've noticed the relief valve dripping a lot.

I believe most faucets in RVs are only compatible with catsup.

dutchmensport · 02-01-2022, 02:11 PM

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

JRops · 02-20-2022, 08:45 PM

Is this possibly why my water heater leaks once I turn it on? I have to shut it off to avoid the constant hot water running down the side of the coach. Keystone says "that's normal". I have a nasty mess in the water heater compartment now after the dealer replaced several relief valves and a thermostat. I bought the coach new in May 2021 and it started this less than two months after I had it. That was also around the time I started living in it full time.

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