Cold sandwich

Mike Dunn

What I mean by "cold sandwich" is the effect you get when you run a faucet for a little while and when you shut off the flow the burner shuts down and a little shot of cold water fills the heat exchanger in the water heater. If you use hot water again within a short period of time you get the hot water left in the pipe, followed by the cold sandwich, then some more hot water. Some ways around this are expensive systems of storage tanks and circulating pumps. I would like to know if there is less expesive way to fix the cold sandwich.

Mike Dunn

Cold sandwich

I would like some suggestions on how to eliminate the "cold sandwich" effect inherant to all tankless water heaters.

[Deleted User]

Splain please....

What exactly is your idear of a cold sandwich. Is it when you just get the water temperature adjusted to where you want it, and your wife turns on the dishwasher and blasts you in the shower with cold water, and you scream, and yell, pounding on the wall of the shower, and she immediately shuts off the dishwasher and you get blasted with hot water... OR is it something else...

ME

Jerry_15

Yeah, splain please - and no, it's not the same on all tankless water heaters. The old models with standing pilot had a rubber diaphragm that is very dependant on flow, but not very sensitive, specially if it gets old or has a pinhole. Under best conditions these would drive you nuts with a single handle mixing valve. Add a low flow shower head and you have a perfect storm. Upon getting your water temp perfectly adjusted the flow rate drops below the min gpm to kick in the gas valve. Cold water. You turn the control to hot the thing fires, water temp gets too hot, you mix it down, bingo it goes cold. Sound familiar? A big **** high flow head, or just pull the restrictor out of the existing one, might solve your problem quick. Replace the diaphagm if it's a few years old, and buy a spare. The new rigs from Rinnai and Takagi,etc., are a lot more forgiving, and can run multiple fixtures easily, but don't work without power, and still require a min flow rate. Good luck.

Maine Doug_28

Oh!

And here I thought it meant when two people were in the shower and the water got cold. Ya learn sompin everyday.

Plumdog_2

Every time the tankless starts up

a little turbine inside starts to spin, then the logic board starts the combustion process. This takes a few seconds, and meanwhile a short slug of icewater begins migrating towards your shower. The term "instantaneuos" is really a misnomer. You can use a small electric water heater and pipe it in to correct the sandwich effect. Your installation manual should show the proper method.

ScottMP

Mike

I too was confused but now know just what you are talking about. This is one of the things that customers will have to be aware of when buying instantanous water heaters.

Also the longer wait for hot water as the flow switch turns on the heat. Where you used to have a wait of a few seconds before the hot water arrives you know will have about ten more seconds. Seems like a small amount if time but when your standing there waiting to wash your hands, its a life time.

I make sure my customers are very aware of the different style of hot water heater they are getting, Along with the fuel savings.

Scott

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Bill Nye_2

cold sandwich

I think tunafish is the worst when frozen PB+J is pretty bad too. You leave for work @ 6:30 and the sandwich sits in yer dinner pail 'til noon in 5 - 10 ° weather, thats a cold sandwich.

If the guys go out for something hot, don't bring the frozen sandwich home. Throw it away or feed it to the dog because your wife won't make your lunch any more if you keep this up. After 23 yrs of marriage trust me I should know.

Plumdog_2

you got that right

no sammich is good after 30 years; but a cold sammich is just intolerable

JackFre

There have been recent changes in the on demand

equipment to minimize, but not eliminate, the "cws". Rinnai has recently introduced a quickfire process which basically puts a giddy-up on the firing process, thereby shortening the cws by a bit more than half. It is a characteristic of the style product and needs to be explained to the customer. Just as you must explain that it is not an "instantaneous" water heater. It is best to call them on demand or continuous flow, IMHO. If you call it instantaeous your customer will teach you one of those unpleasant lessons when they don't get it.

Tony_23

The other day,

I had a Cool Water Sandwich and a Sunday go to Meetin' Bun, bow bow bow.

Sorry, couldn't help myself

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John Starcher_4

Bow Bow Bow.............

Jerry_15

Have you tried the high flow shower head yet? Cheap fix, feels good too, live it up. Course you may spend more time in the shower.