Water Heater Issue

[Just_Jeff]

Hi - I'm having an issue with my Atwood propane on-demand water heater. When we turn on the faucet, the water cycles between very hot and cool. It's like the hot water heater works for a few seconds, then doesn't, then comes back on. I think it's buzzing louder than it has in the past, too...but I don't quite remember. And when we turn off the faucet, it continues buzzing for a bit...again, I don't think it did this before either but I'm not positive.

We are on city fixtures right now so it's nothing to do with the water pump, and the propane tank is 2/3 full.

Any ideas?

[Just_Jeff]

Might have figured it out...I'm away from the RV at the moment but had my son test out a few things.

- When the kitchen faucet is on full hot, it doesn't cycle.
- When the bathroom faucet is on full hot, it doesn't cycle.
- When the shower head is on full hot, it cycles.

That leads me to believe that it's a flow problem...the water needs to flow at 1.5gpm (I've read...assume it's the same on mine) to keep the hot water heater turned on.

But here's the weird part.
- When the bathroom sink AND the shower head are on full hot, it still cycles...even though the sink apparently had enough flow by itself to prevent cycling. I'm going to test this again when I get back just to confirm that my son understood correctly what I was asking.
- When all three faucets are on, it doesn't cycle.

I thought one possible fix to this would be to reduce the temp coming out of the heater, so that a comfortable water temp would require more input from the heater...but that didn't work. My son said he couldn't feel any difference in hot water temp when the thermostat was turned all the way up and all the way down. That may just be b/c it was too hot in both positions, so I'll confirm with a thermometer. That could be an indicator that the thermostat isn't working correctly.

Still welcome any input or suggestions!

[Just_Jeff]

Nope - same thing on pump. The heater cycles on and of every 10-15 seconds. I had my wife turn on the hot water while I watched the heater, and I could hear it turn on and off. My wife confirmed that the water got hotter and colder as it cycled.

The pump has always given us adequate pressure before, and the pressure from the campground seems to be fine when we use it for the sink and such.

Any other ideas?

[Just_Jeff]

Interesting. I'm on CG water now so I'll try switching to the pump and see it it changes anything.

[donn0128]

Thats a different story. From what i have read the problem you are describing is quite common. The biggest cuplrit is low or irratic water pressure. Those things are fine for brick and mortar houses where the water pressure is pretty consistent. But in an RV where water pressure can vary a lot not so good.

[Just_Jeff]

Thanks. It's an on-demand heater so there's no tank or winterizing valve. Not sure about a check valve...I'll look for one when I get back to the RV. The burner is at least burning for part of the time. Not sure why it cuts out, though.

[donn0128]

Winterize valve partially closed? Bad check valve at the water heater. No air gap in the tank. Lots of possibilities. Start by turning off the heater and the water. Drain the tank. Close the drain and turn the water back on. Go inside and turn on the how water faucet until no more air. Turn on the heater and wait until it is hot. Try again.
Have you actually checked to be sure the burner is working correctly?