New water heater, shower hot then only warm water in 5 minutes
I installed a new water heater and have hot water in the kitchen on the first floor. On the second floor in my bathroom shower, the water starts out hot but in 5 minutes, the water comes out only warm. My bathroom sink is the same way. I don't believe I have lost any water pressure. I have the same brand, type and gallon capacity as my other water heater.
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if it has been constant from instalation it might be that ur shower head is rated too low to get enogh gpm ( gallons per minute) it will tell u most of the time around the shower head where it threads onto the spot of the wall what the gpm is. alot of the energy saver heads are restricting tehgpm to 1.5 or .5 gpms to conserve water well the water heater will only operate correctally around .5 gpm depending on model so if u are not pulling enough water u will not turn the water heater on to get ur hot water all the time so go to lowes ( or locally trusted hardware) and get a new shower head make shure u look for the gpm on teh head and check in ur owners manual to see what gpm ur water heater kicks on
P.S. if ur shower head is rated at higher gpm say 1.5 and it is corroded or pluged up say with lime it is going to restrict it causing a lower gpm
I had the EXACT same problem (installed my tankless last winter and worked fine, now this summer it fluctuates, have to turn the shower completely off and then on again to get any hot water and then it only lasts for a couple of minutes!) Argh - it is frustrating!
Here's what I found: the demand for hot water is lower during the summer (hot) months because the "cold" water coming in is already quite warm. You don't need as much hot water to make the shower temp comfortable. SO, my tankless was shutting off due to low flow demand. I've removed the flow restrictor from my shower head and it helped alot but didn't completely solve the prob. Next step is what has been recommended to me by several people but is much more expensive - change the pressure valve on your shower to a temperature valve. Or just wait til winter and it should work ok again :)
Problem new or old? How long you have unit? Sounds like not enough flow to keep burner on. Tankless need at least .6 gpm to keep hot water flowing or else the burner fires then shuts fires then shuts and you get a sandwich effect...hot cold hot cold. If you have new diverter valve in shower -vs- old two handle type try turning hot water ALL the way ON and see if hot stays hot. If it does stay hot then slowly adjust to cool and see if you maintain a good MIX for proper temp. If it goes cold again try this......LOWER control pad setting to a comfortable 105 degrees (ladies) 100 degrees(men) and turn shower valve all the way to HOT. See if your temp remains consistant now and if it does then problem solved. Tankless mindset...set temp on control pad and stop trying to MIX at shower valve. Thats how these things work. Thats why I install a control pad in each bath and one in the kitchen for adjusting ash temp during dishwasher on time. ditto for wash machine. You should never need to turn on cold water if your unit is set to proper temp at controller. Hope this helps
A 40 gal. electric water heater will give you aprox. 32 gal. of hot water in one setting, since they do not reheat as quickly as gas. So if you are using a newer 1.5 or 2.0 gpm shower head. You could take a 16 minute shower with straight hot water. If you are running 2 new shower heads at once you could get 8 minutes. If you using the tub spout the times decrease. Some of my customers like to turn up the temerature on the thermostat a little so they can mix more cold and get it to last a little longer. Be very careful doing this.
If your water heater has a lot of calcium built up in it the times will decrease.
With out seeing the heater, you mention it is a mobile home heater so I am guessing that it is bottom fed.
I hope this has helped.
Will the water stay hot in the kitchen sink? Try to isolate the problem. If it is happening at all hot water locations, then it will be related to your water heater. If just in the shower then it is related to the mix of water ratio coming out of the shower hear. If its only the shower, then you are getting too much cold and not enough hot through the pipes. This can be very simple to fix by replacing the handle going to the shower. If this does not work then you may have a problem in the hot water pipes. After you isolate the problem, please post another question here.
I think the dip tube in your water heater has failed, this is a plastic tube that goes in the cold side of your tank and forces incoming cold water to the bottom of the tank allowing hot water out at the top. When this tube deteiorates the incoming cold water mixes at the top of the tank causing the problem you have. the dip tube runs about 5 bucks but takes someone with pluming skills to install.
I found a way to get warm water in the shower, but I'm not sure it qualifies as a solution. After trying everything else I thought that maybe when I was feathering the faucet in the shower toward the cold side so I would get warm water that at a certain point it blocked the flow on the hot water side enough so that the sensor in the hot water heater sensed there was no demand in the line and it shut the water heater off. To test this, I went to the kitchen and turned the kitchen sink faucet all the way to the hot side and then turned it on so that I got a small flow of water. I waited for the water to get hot to be sure the hot water heater was working. Once it was hot, I left it running to keep demand in the line and then I went to the shower and turned the faucet on. When the water got hot I started feathering the control towards the cold side and soon I had warm water. So I think I'm right in that the sensor in the hot water heater was shutting the water heater off when the demand in the shower was lowered to a certain point when I was trying to adjust the water temp in the shower.
So now I can get warm water, but it means I have to leave the hot water running at another fixture in the house to create a false demand in the system so the hot water heater doesn't shut down. Is there a way to adjust the senor in the hot water heater so that it will stay on when I'm using the shower only, so I don't have to waste water by running another faucet when I want to take a shower?