Hot water, over-pressurization

Hey guys,

2016 Grandby Fd. I've noticed that the hot water line below the sink will leak after firing up the hot water heater for the first time in a day or so. I'm assuming enough time for the water in the tank to cool down. Once the water is freshly heated, it has obviously expanded in the tank and system forcing some hot water past the fittings below the sink. I can keep the fittings from leaking if I open the hot sink valve and let a little water out a few times while it's being heated. The pressure from the sink is obviously higher than usual for just a second or so. Until it's been relived.

Is this normal, or is there a pressure valve or something plugged up or not functioning someplace?

This is pretty normal. My hot water heater is always a little over-pressure after we first heat it up. The issue is that the hot water heater has some air in it, which expands a bunch when you first heat it up, causing the overpressure.

Interesting problem,
I seldom use my hot water tank, but I will look next time I do.

I'm assuming our tanks have the ability to regulate how "hot" the hot water gets heated. Perhaps dealing it down a notch will eliminate your issue and still give you desirable hot water temp.
If not, it sound like your solution of opening the hot water tap a smidgen is what you will have to do.

There is supposed to be a bubble of air in the water heater, it allows for expansion as things heat. If it's too full, you can get leaking, but it's usually at the over pressure valve. Because your leak is in an inline fitting, I wonder if some Teflon tape is in order.

I'll edit this to add the link for the bubble... http://www.rv-motorhome-answers.com/RV-water-heaters.html

Thanks for the feedback guys. I was just wondering if it was normal. Looks like we'll just keep cracking the valve as it heats.

That weeping under the sink doesn't seem right. I know some weeping at the pressure-relief valve is considered normal operation but I can't imagine it's part of the design for the pipe fittings to weep.

My first thought would be to call FWC and Atwood. But I bet the first question they'd ask is whether you've gone through the procedure to establish the air expansion space. I see the user manual recommends you work the pressure-relief valve once a year anyway so I don't see any downside to going through the procedure.

The procedure in the link in post 4 says...

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Reintroduce an adequate air expansion pocket and this is how it is done:
1. Turn water heater off.
2. Turn off water supply (city H2O or H2O pump)
3. Open closest hot H2O faucet in RV.
4. Open the P&T valve by pulling on handle at end of valve and allow H2O to flow until it stops.
5. Release handle on P&T valve – it should snap shut. ( do this a couple of times as it may stick)
6. Close hot water faucet.
7. Turn on H2O supply – Now that everything is closed the tank will refill and air expansion pocket will be re-established.
Repeat the above procedure if P&T valve continues to weep between heating cycles. If this is not successful then the P&T valve should be replaced.
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It's very similar to the one in the user manual. Please note, though, that it fails to include the anti-scald warning. That warning says "Turn off water heater before opening pressure-temperature valve to establish air space. Storage water must be cool". The step-by-step procedure should include another step: "Allow water to cool".

I'd try the procedure and see if it resolves the problem. You might also try measuring the temperature at the pressure-relief valve with an infra-red temp gun to see if it's allowing the temperature to exceed its design temp of 150 degrees.

Also- The language in the user manual suggests it's to be expected that you'll occasionally need to re-establish the air space. It also has a more permanent solution to the problem for those interested. If you look at the bottom-right of page 5, you'll see it recommends adding either a pressure-relief valve or an expansion tank in the cold-water inlet line to the water heater. If you get to that point, there's another question for FWC or Atwood-- can you recommend a valve and/or tank?

Also- The water heater's thermostat is not adjustable but Atwood does sell an adjustable replacement one. That's an option for anyone convinced their water heater just gets too hot. But it does mean your hot water wouldn't last quite as long as you'd be mixing less-hot water with cold as you use the sink or shower.