Water Heater Suddenly Only Produces Warm Water

Submitted by PernPorson t3_ydldzs in DIY

Just noticed yesterday that our water heater is only putting out warm water. I chalked it up to colder outside temperatures? But it warmed up today, so that'd definitely not it.

I got to doing research and investigating and found the following:

-Pilot light is on.

-Burner is on and visible.

-All sinks and faucets produce only warm water.

-Pipe on top of the water heater only gets warm.

My research and investigation lead me to thinking that it's a clog, sediment, or a broken dip pipe, bit I'm not really sure how to check the last two or where to check for a clog since it seems like it would be inside the heater itself. My research has left me empty handed on how to safely troubleshoot these potential issues.

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UserD61 t1_itswl03 wrote

You may have an issue with your thermostat

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PernPorson OP t1_itswnqk wrote

Any idea on how I could check that?

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UserD61 t1_itsx0w3 wrote

Unfortunately, no. I only suggest it because that was the issue with mine. I didn't DIY that, though.

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novakunad t1_ituho6v wrote

Depending on the hot water heater there is an adjustment for temperature. Normal ones are set to about 120, when I lived in upstate NY we set it to 140 because of the 40F water coming in. You had to be careful when using the hot water but it was never warm unless you had the cold on.

Pictures go a long way on the internet.

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usedTP t1_ituxpwx wrote

Turn it to warmer and see if it fires off.

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No_Football_6143 t1_itsx8zg wrote

There are usually reset buttons on gas water heaters for the thermostat. The reset button is often red and located near the thermostat or behind a metal panel that is removable on the unit. When you find it, push the reset button and then release it. There may be a lower thermostat button also known as a second reset button.

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muckpucker t1_itu7yzu wrote

This only applies to electric water heaters, not gas.

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PernPorson OP t1_itsy7zn wrote

Cool, I'll go try that one. Do I need to do anything beforehand? I know if you're restarting the pilot light, you should drain the tank. Is there anything like that that I'd need to be aware of?

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Wellcraft19 t1_ittl3ce wrote

You should not drain the tank if restarting the pilot light. In fact, you should NEVER lit anything with a drained tank. That said, have you tried draining out the sediment that accumulates at the bottom of the tank (more if tank if starting to rust)? I drain the sediment out of my tank about once every two years. Essentially nothing. I also replace the sacrificial anode at intervals.

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TerritoryTracks t1_itu1kgx wrote

No you should not drain the team when restarting the pilot light. Absolutely not. Not sure where you got it from but it is utter nonsense. Sounds like something a disreputable tradie would say to make it seem like you have to call a plumber just because your pilot went out.

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No_Football_6143 t1_itsyg5t wrote

Not for this. A simple push of the button should do. I have restarted and relit my pilot light without draining the tank with no problems. How old is the water heater?

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PernPorson OP t1_itsynmd wrote

It's not super old. About 10 years, but the house was vacant for 4 of those.

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No_Football_6143 t1_itsz06h wrote

Well the good ones have a life expectancy of about 8-12 years. My last gas water heater lasted right at 9 years before I had to replace.

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PernPorson OP t1_itszoc1 wrote

😔 we were hoping to get a little more time with it.

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Wellcraft19 t1_ittl670 wrote

I’m on year 21 and expect to get an additional ten years. All about preventative maintenance.

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Lanoir97 t1_itu7vtr wrote

What exactly do you do as preventative maintenance? Cleaning the tank and burner?

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Wellcraft19 t1_itx1eq4 wrote

Draining the bottom to empty eventual accumulation of sludge on an annual basis - and replacing the sacrificial anode (that is supposed to corrode, not your tank) as needed. "As needed' depends on your water. Can be anything from every two years to once every ten years.

The sacrificial anode is $15-$20 in most cases and relatively easy to inspect and to replace. In my case even with limited headroom above the tank, managed to pull out the old - not badly corroded one - and insert a new one. No need to empty tank, just drain it a tiny bit to ensure water does not leak out the top when anode is removed.

Still, I think that is a task that 99.99% of users never undertake, as we are taught that hot water tanks are 'install and forget' and only 'should' last 5-10 years.

I do inspect burner if via the opening, try to ensure no dust has accumulated underneath (have pets, dust occurs on basement floor). I try to keep tank clean and dust free on the outside, make sure flue and vent hood are properly connected and in good shape, etc. Same goes for the china cap and B-vent exposed to the outside elements.

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PernPorson OP t1_itt0kiu wrote

Well it appears that mine doesn't have a reset button. It's a Honeywell WT8840B1500. I read some weird stuff on Google saying I have to turn the knob to a few different positions, but that didn't do anything...

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No_Football_6143 t1_itt0u91 wrote

Sounds like an older model. May be time to replace then. It’s definitely not clogged or anything like that. If so you would have pressure problems when turning on the hot water. If you can’t afford a new one, watch a video on how to clean the sediment tank and attempt that, I should caution you that doing this on a gas system is risky if you are not well versed in this area.

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PernPorson OP t1_itt1273 wrote

I'll call a plumber out before I go that route. We're not strapped for cash, but we were saving for some other expenses.

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imnotsoho t1_itt4kfp wrote

Have you tried draining and flushing it? If the burner is running, maybe there is major sediment at the bottom not allowing heat to get to the water.

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PernPorson OP t1_itt5ah5 wrote

I'm not so certain the burner is on anymore and flushing it will be the last thing I try. That's a lot of work and I don't have the time to handle that right now.

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Sfwupvoter t1_itud3c3 wrote

You should easily be able to hear the burner turn on. If it isn’t turning on, that limits your problem areas.

If it is not turning on there is only one other thing I can think of, which is the flame sensor. Basically look at the pilot flame, there should be a metal rod in the flame. That is a sensor designed to heat up trip a signal. If that signal isn’t tripped, the system can’t run.

It is a very common issue. Super cheap part.

You can diy fix by either replacing or taking some sandpaper to it if it looks scorched. Sometimes it builds enough carbon on it to insulate it and not allow the main flame to come on. Either way 5 minutes work, maybe 15 if you really don’t know what you are doing. Does require turning off the pilot.

You should take the opportunity to flush the tank as well. That’s simply just draining the water through the hose bib at the bottom. Sediment builds up an can be an issue. Should be done once a year. Must be done with the flame off though.

Procedure to do that is turn off the incoming and outgoing shutoffs. Turn off the pilot. Open the pressure valve (weird lever thing on the overflow pipe. Make it stick straight out). Then attach a hose to the bib and lead it to a drain in the floor. Open the bib. It will take an hour or so to drain and it will pull the sediment at the bottom with it.

Once done turned on the supply to get s few more gallons in the bottom and drain that. Just to get everything out. Then close the bib and turn on the supply. Fill until a bit of water comes out the overflow and close the over pressure valve. Then give it about an hour to settle and open the shutoff connecting the system to the hot water supply.

The hour to settle is really important. Otherwise you will get bits of calcium and the like in your faucets.

This process should be done once a year in most areas with medium to hard water.

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Zed-Leppelin420 t1_ittfogy wrote

Check the dial at the bottom. I once rubbed against it and turned it way down to like warm instead of hot

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wasachrozine t1_itv6q56 wrote

If you do end up replacing, consider a heat pump water heater if you have space. Will save you money.

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Gobucks21911 t1_ittg0fv wrote

Sometimes they can just replace the control panel and not the whole unit. You could ask about that. Ours said the control panels go out before the water heater does.

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Zerobeat50125 t1_itszhie wrote

Top-filling tanks have a dip tube, which routes the incoming cold water to the bottom of the tank. They can become damaged or detached, allowing cold water to dilute the warmer water in the top half of the tank. They are easily replaced, just remove the incoming water supply nipple. Some tanks combine the anode rod with the dip tube, but if not, this is a great time to replace that, as well.

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odonk_ t1_itt2cox wrote

Definitely check the dip tube before buying a new water heater. Much cheaper and easier.

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iSOBigD t1_ittdhqw wrote

Yeah, agreed I can confirm I had that issue. I got a plumber to look at it and it was fixed in 30 min.

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pentasyllabic5 t1_itul6or wrote

While you are doing all of this

  1. Flush the tank if you have a way to. This should be regular practice if you had it or if it is plumbed in a manner consistent
  2. Per the post above Read about "Anode Rod Replacement". You should plan to do that too. It's easy given what you are about to do and who wants to disassemble in a year or two for it.
  3. Ensure the burner flame is proper. There are videos online that show how the flame should look. Just because it is lit doesn't mean it's working right
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thesophisticatedhick t1_itu6hjz wrote

This has happened to me a few times. I have traced the problem to a drop sink in my garage which has a spray nozzle like you’d find in the dish pit of a commercial kitchen/restaurant.

There are separate valves for hot and cold that blend into the faucet and the sprayer. The faucet has a valve which can be closed to send all of the water through the sprayer. Usually, when I am not using the sink I leave that valve open and turn off the hot and cold valves individually, but every once in a while I forget to do that and i leave the hot and cold open, closing the valve to the faucet instead (leaving the line to the sprayer charged).

Whenever I do this I get warm water from the hot taps around the rest of my house. I think the cold water supply has more pressure than the hot and it’s forcing it’s way through the valves in that drop sink and lowering the temps in my water heater. This has happened a few times now and it’s the first thing I check if I’m not getting hot water in my kitchen or bath.

I hope I explained that well enough. It’s 3 AM.

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funkadunk8 t1_ituvlrx wrote

I had a tub with a bad mixing valve and my water would be warm until about 10-15 minutes in once it’s heated all the cold water in the pipes too haha

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mostlygray t1_itszx6h wrote

If the thermostat reset doesn't work to make it run the right temp, listen to the water heater as it heats up. Does the water heater make a boiling sound when it's running? If it's doing that, you've got huge amounts of sediment at the bottom and that can be helped for a little bit.

Turn the thermostat off and run the hot water until it runs cold. Then you can open the drain at the bottom to empty the water heater from the bottom. There's a garden hose fitting on it to run the water into a floor drain. Flush it with cold water a few times and the water at the bottom should come out full of crystals. Keep flushing until you stop getting crystals of sediment.

Close the valve. Refill the tank. Set the thermostat to "A" and let it heat up. If it runs hot now, that was it. It does mean that the water heater is on it's way out, but you can squeak another year or two out of it by draining out the crud.

The gas company in my area has service that basically puts a lifetime warranty on all appliances. Furnace, water heater, washer, dryer, fridge, whatever you want. It's a reasonable price and will save your ass in the winter. If my furnace goes out, I'll have a repair tech out to my house at any hour. They've come out at 1AM before. If you can get it, everyone should use a service like that. I've used the service many times on my terrible old appliances.

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PernPorson OP t1_itt0njn wrote

OK. We're not getting any boiling sounds, only a slight hiss. Should we still drain it?

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mostlygray t1_ittc9m7 wrote

If it's not doing the crazy bubbling thing, I wouldn't. Sometimes that type of valve won't shut all the way again because they hardly ever get moved. I've only done it because it was the only way to keep the water heater working and there was no loss if it didn't work.

It's worked the 3 times I've done it on 3 different water heaters but I'd hate for you to do it unless it's a last ditch effort. All three of those made that distinctive boiling noise. You know it when you hear it. It really stands out as weird.

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chuckfr t1_itt5fr5 wrote

From the discussions, it sounds like you’re going to want to replace this.

If you do, check your local utility for rebates. I was able to get a $500 rebate on a much more efficient model that wound up being just under the price of the less efficient one.

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PernPorson OP t1_itt7ewc wrote

Good tip. I just checked my energy providers rebate program. They have one, but the funds are all used up for the year.

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kid_wonderbread t1_itt94lz wrote

Have you drained it lately? Should be done at least once a year. I'll notice my hot water won't last long then drain it and it starts working like it should again.

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NotObviouslyARobot t1_ittl96s wrote

That's probably busted heat trap. Source: Have had this happen on water heaters on properties I manage. You can get new heat traps at Lowes or home depot. They're basically one way valves, but the gist of it is, they stop your hot water from getting into your cold water inlet

Alternatively, it could be a failed fixture

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RenzoARG t1_itu2jye wrote

Air bubbles in the pipes can also give you warm water as a result. Either that or sediments:
"water heater purge" at google has the solution for you.

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danielthechskid t1_itu5px5 wrote

These Honeywell/Resideo WV/WT8840 series valves can be problematic. The older ones had an all plastic thermowell which would get old, craze, start leaking water, and then the water would damage the dual NTC thermistor that senses the tank temperature and cause an error code 5 which disables the main burner for safety since the control can't be sure of what the actual temperature is. That's why it's a dual thermistor and not a single one as usual, it compares the 2 and if they don't closely match it faults out.

That's what happened to mine, the WV8840B1059. I had the same barely lukewarm water issue and a code 5 sensor failure along with eventually a damp spot below the control where the water was occasionally dripping. I replaced it with the WT8840B1500 which has the metal cap on the thermowell to protect it and hopefully stop it from ever leaking.

You said that yours already has the 1500 on it, if anything is wrong it should be blinking a trouble code.

Oh and do also check your anode rod, it has nothing to do with it not heating but it is extremely important, I picked up a free water heater that was identical to mine to practice the gas control removal on before I did my own one. It had rusted out and leaked because the anode rod was corroded away entirely, the best part, it was 2 years newer than mine and yet mine is still fine because the anode rod is only about 50% gone (I removed and checked it while the tank was drained), I guess I have lower TDS water or something.

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Reelair t1_itu5yza wrote

An easy test to check the dip tube is to open the drain on the bottom of the tank, open it quickly and open it a few turns, you want good flow. If the dip tube is good, you should get cold water after a few seconds , if the tube is bad, you won't get cold water.

The dip tube brings the cold water to the bottom of the tank where it get heated. If it's faulty, the cold water goes in at the top of the tank, then out the outlet line, giving warm water instead of hot water.

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CatnipAndLasers t1_itu9l0f wrote

Most likely the dip tube.

Also, I havent seen anyone ask if you have a mixing valve on the outlet pipe. Here in canada they're code and often the source of fluctuating or lukewarm temperatures. Replacing them is easy if you buy the exact same model.

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turiyag t1_ituc13a wrote

If you do have to get another one, don't rent one, buy it. The cost of renting vs buying is about 4-7x as expensive. I don't understand why some places rent them so hardcore.

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Jabbatheputz t1_ituggrt wrote

Replace the dip tube, It supplies the water to the bottom of the tank. Most of the time the tube breaks down a falls apart letting cold water into where the hot water reservoir is. It’s less than $10 to fix it

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Perused t1_itsvhna wrote

Did the temperature knob accidentally get turned?

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PernPorson OP t1_itsvtv5 wrote

I doubt it. It's on a scale of A->B->C and it was at B which is above the recommended settings. I moved it up to B and a half and got no change from it.

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NumberNumb t1_itsxj93 wrote

I have a vent on the top of my water heater that sometimes sticks, and the burner won’t click on. Couple heavy knocks with my hand and the flap is free to move again the burner fires right up. Worth a try.

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PernPorson OP t1_itsy00g wrote

I'll keep that one in mind, but my burner is lit. I can see it from the little window.

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GONZnotFONZ t1_itt1zvv wrote

You can see the burner or the pilot? If you turn the temperature knob all the way up does it then kick on?

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PernPorson OP t1_itt2tzf wrote

You know... I'm second guessing myself. Pretty sure I'm seeing the pilot, not the burner. I may need to dissamble a little more to see the burner assembly.

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GONZnotFONZ t1_itt36iw wrote

If you turn it off, relight the pilot, and turn the temperature knob up you’ll be able to hear the burner kick on. If it doesn’t, it’s probably something with the thermostat. If it does and it still is producing warm water, then the unit might just be bad.

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PernPorson OP t1_itt472a wrote

Gotcha. I'll restart it tomorrow. If it turns out to be a bad assembly, would you expect anyone could change it safely? I know my way around a toolshed, but I don't want to blow up.

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jeffersonairmattress t1_itt6oja wrote

I don't think your burner is lighting at all. You can prove that the warm water is just leftover by just letting it run and finding it eventually just cold.

Nobody has mentioned a thermocouple. That's the easiest and most common fault of a gas DHW heater. Google thermocouple replacement. No need to drain the tank. Just turn black knob to off, slide access panel open, re and re thermocouple, then follow instructions to re-start your controller (typically turn black knob to pilot, press and hold and light pilot while new thermocouple heats, turn black knob to on, hear satisfying click and whoomph, close access panel)

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PernPorson OP t1_itt7ast wrote

I'm thinking this is it. I just turned the pilot light off and tried to restart it, but the thermostat isn't detecting it. Surely that means the thermocouple is bad. I'll rip it apart tomorrow and check.

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Gobucks21911 t1_ittfsju wrote

I’d call a reputable plumber. Just had ours looked at for a vent flue issue and initially he was thinking it would need to be replaced (done rust). But he was pretty quickly able to identify the issue and fix it for a couple hundred $$ instead of $3k, plus I didn’t have to worry about natural gas explosions, lol.

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Nefarious_Compliment t1_ittl10o wrote

Get it serviced. The burners might be acting up, it might have a bunch of debris inside, it might have venting issues.

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Beowulf44 t1_itu5tvt wrote

Isn't that the main point of its primary purpose?

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blackpony04 t1_itu61wb wrote

Bad news OP, your water heater is very likely at the end of its life at 10 years. And expect to spend about double what you think it should cost because I had major sticker shock when mine crapped out in May. My old one was 12 but it was a power vent version and it cost me $2k installed which isn't too far off from the cost of tankless. I knew mine was aging but I had hoped to stretch mine 6 more months so I could budget for it as I already had to replace my fridge a month earlier. The last water heater I replaced was 15 years ago and that was the standard chimney vented one and it was only $600.

My house is 12 so I'm now budgeting to replace the washer & dryer and the furnace next year (I've already been told I'm pushing that now as the builder apparently installed a shitty one). It never ends....

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Beneficial-Shower-42 t1_itv0jbt wrote

How old is this water heater? Gas heaters will usually last 8 to 12 years. If you do routine maintenance to the burner anyway.

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Drknss620 t1_itvvr5t wrote

Gas tech here. As others have mentioned before about the rod , this can be the case , typically you can also tell this is happening because your gas bill will go up since the tank will keep needing to run in order to be satisfied, but if you notice your gas bill going down in terms of therms used , it could possibly be the thermostat itself is bad and is stuck or broken , basically when this happens the burner won’t stay on long as the heater thinks it’s at the desired temp too soon, you can replace the thermostat typically you buy the entire control , and replace it

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series_hybrid t1_itw1hqj wrote

Th we other posts are the most likely culprit.

That being said, it's useful to add pipe insulation from the water heater on all the hot water pipes.

Water heaters have factory insulation, but adding a wrap around it that is designed for that will make it cycle less.

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luchadorhero t1_itt2nas wrote

could be the heating element, im pretty sure there is 2. you probably have one that just ate away and melted.

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Verdin88 t1_ittox72 wrote

He has a gas water heater

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luchadorhero t1_ittzi4x wrote

I wouldn't know, I would know i've replaced 3 of them in my life. And if OP doesn't have them its a harmless suggestion and would have saved hundreds.

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