I have had a tankless gas hot water heater for 2 years. There are a couple of things that bug me about it but mostly I like the continuous hot water it provides and low operating cost. One problem that drives me & my 89 year old mother up a wall is the cycling of hot and cold at start up every once in a while. I have stood by the shower testing the water for over 10 minutes until it decides to make an even heat. Turning it on and off eventually corrects it. Does anyone know what the problem is? MY plumber doesn’t know and the manufacturer was no help. From the last issue of the magazine showing how the tankless HWT heater works I would guess there is a problem with the gas valve. Mine just happens to be Rinnai. I hate hearing my mother swear.
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Cycling on and off usually indicates that the flow of water past the sensor switch is at the minimun required to activate the heater. This is the reason why I hate tankless heaters -- the sudden shock of the hot water going cold.
My solution was to run the hot water at the sink to increase the flow of hot water, which keeps the burner on. The wasted hot water down the sink negates any energy savings, which is also exactly what I discovered.
Thanks for the info. Will try it.
Alg
I have a tankless water heater and I absolutely love it. Would never have anything else again. BUT, lately, the pilot light goes out sometimes when I turn on the shower. I have to go fire it up again and it's fine. It doesn't happen with any other items (dishwasher, tub, faucets)....just the shower. It's like the sudden rush of water blows out the pilot light. Wierd. Any thoughts on that??
Jeannie
I'm guessing it's a modulating burner, and the shower demands full heat right away. Simple "fix" is to run the shower at 1/2 volume for about 30 seconds before turning it on fully (or just run the sink for a similar time). As to the actual cause, it may be that the gas valve is sticking and needs replacing, but that's just a thumb suck.
One issue we've seen on a few occasions: the pressure-drop through a tankless water heater is fairly steep, which creates a pressure-differential between the hot/cold water lines in the home's plumbing system. Mother Nature (another mom!) hates an imbalance and looks for ways to even out the pressure. There's typically only one cross-connection between hot/cold in a home - the ACW solenoid valve.
Try turning off the water-valve to either the hot or cold (or both) feeding the washing machine. Then see if your mom drops the sailor's language when using the bath!
The solenoid valves in washing machines are designed to regulate cold/hot flow, but can allow cross-migration. We've seen cases where there was sufficient pressure-imbalance to induce cross-migration that caused the tankless burner to "flutter" on/off as cross-migration-flow through the ACW solenoid short-circuted cold-to-hot and reduced flow through the tankless.
If that turns out to be the root cause, a soft-seated check-valve can be installed in the hot water line feeding the ACW to stop the reverse flow.