Water heater going hot and cold with weird refill noises
Old water heaters can experience erratic temperature swings, long periods of running cold after heavy use, and strange refilling cycles. These sudden failures leave you without reliable hot water and make standard maintenance risky due to severe internal calcification, forcing homeowners to question whether to repair or replace the failing unit.
What the numbers show
Counted from the threads quoted below. How we count
- Most of it landed at once — the busiest month was September 2026, with 25 people.
- This comes up 12.7× more often in r/Plumbing than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1replacing the entire water heater unit2 people mentionedDid this help you?
- 2trying to DIY repairs on gas componentsDid this help you?
- 3replacing failing parts like gas valves or thermostatsDid this help you?
- 4Contacting the previous owner to ask about the maintenance history and checking the condition of the drain valve.Did this help you?
- 5Cutting and coupling the PEX pipe back togetherDid this help you?
- 6Unscrewing the hot dielectric nippleDid this help you?
- 7Leaving the anode rod unservicedDid this help you?
- 8using emergency savings fundsDid this help you?
- 9Switching to an electric anode rodDid this help you?
- 10Inspecting the anode rod yearly if using a water softenerDid this help you?
- 11Putting a Tupperware container under the leakDid this help you?
- 12Running a dehumidifier in the basementDid this help you?
- 13Calling a plumber for an inspectionDid this help you?
- 14Budgeting for an early replacementDid this help you?
- 15Leaving the water heater unflushed to avoid potential damageDid this help you?
- 16Considering a single repair option instead of replacement if the unit is not leaking.Did this help you?
- 17Trying to flush the unit and inspect connections to figure out if an anode rod was installed incorrectly.Did this help you?
- 18leaving the water heater alone and letting it run until it failsDid this help you?
- 19saving money for a future replacementDid this help you?
- 20replacing only the anode rod while skipping the flushDid this help you?
- 21setting up protection near a sump pit in case of leaksDid this help you?
- 22Hiring a plumber to replace the unitDid this help you?
- 23Buying a shorter model to fit spatial constraintsDid this help you?
- 24Replacing the rusted gas shutoff valveDid this help you?
- 25shutting off the water supply and gas to the unitDid this help you?
- 26using buckets or garden hoses to divert leaking water away from damaging structuresDid this help you?
- 27draining the remaining water from the tankDid this help you?
- 28Replacing the corroded expansion tank with a new oneDid this help you?
- 29Adding a hanger or rack to support the weight of the tank and relieve stress on the pipe jointsDid this help you?
- 30Putting a plastic cup under the pipe to catch waterDid this help you?
- 31Ignoring minor discharge from the pressure relief valveDid this help you?
- 32Replacing the entire unitDid this help you?
- 33Turning the tripped breakers back on repeatedlyDid this help you?
- 34Getting quotes for total replacement costing around $4500Did this help you?
- 35Considering flushing the tanks and replacing anode rods, heating elements, and thermostats oneselfDid this help you?
- 36Buying a flush kit on Amazon and performing the descaling process oneselfDid this help you?
- 37Letting the unit ride without maintenance until it fails and replacing it laterDid this help you?
- 38Signing a liability waiver with a plumber before having an overdue descaling performedDid this help you?
- 39Circulating white vinegar through the system using a cheap submersible pump and washing machine hoses for about an hour before flushing with fresh water.Did this help you?
- 40Turning off power and hiring a plumber or electricianDid this help you?
- 41Replacing the heating element instead of the entire tankDid this help you?
- 42Buying a new water heater unitDid this help you?
- 43Replacing the T&P valveDid this help you?
- 44Installing an expansion tank to handle water expansion from high pressureDid this help you?
- 45Shutting off the water supplyDid this help you?
- 46Turning the temperature dial down to lowDid this help you?
- 47Installing an expansion tankDid this help you?
- 48Checking static water pressure and installing a pressure reducing valveDid this help you?
- 49Keep an eye on itDid this help you?
- 50Put a bucket under itDid this help you?
- 51Tap away at the rusted metal to check its stabilityDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“My electric water heater leaks above the upper thermostat/electrical compartment, but only when the cold water supply valve turn on..”source ↗
“Awesome, RIP to the $800 I was saving toward a new graphics card. My water heater saw my bank account and said, "That's mine now."”source ↗
“My water heater is 2 years old and I don’t know if it’s been flushed before (probably safe to assume not because previous owners were not very good with maintenance tasks). My question is, is it risky to flush it now? Or is it new enough that it should be okay?”source ↗
“I've shut off our water heater, and I have a plumber coming out tomorrow morning to replace our current 40gallon heater with a shorter 40 gallon.”source ↗
“we don't have much space to drill a hole higher in the chimney to reroute the current exhaust.”source ↗
“I'm admittedly out of my depth with a lot of this stuff”source ↗
“Installed a new water heater 3 years ago. It came with an aluminum rod. This is what was left of the rod when I removed it.”source ↗
“I’m unsure of what, if any, maintenance was done by previous owners over the years, but a plumber that came out for a different issue looked at the hot water tank and strongly advices against flushing it or doing any other main tender due to its age and calcification.”source ↗
“Is that sound advice? He was very pushy about advising I replace it now due to its age, so makes me question his advice on maintenance.”source ↗
“I’m a new homeowner and started getting black specs in my hot water. I’m flushing the tank and finding black specs in here. Maybe it’s the anode rod, maybe not.”source ↗
“How am I supposed to service the anode rod with this sort of set up? This particular tank has the anode rod as part of the hot water supply.”source ↗
“Found this morning. Is the small leak or staple something to be worried about?”source ↗
“Turn off gas pilot to water heater. Turn off main water to water heater”source ↗
“Start redirecting or capturing that water so it stops damaging stuff. Shut off the water to the tank.”source ↗
“We noticed we didn’t have hot water this morning, and when we checked the breaker the switch for our water heater had been flipped. When we went out to inspect it, it looked (and smelt?) burnt?”source ↗
“since we moved in, we’ve intermittently had an issue with the water heater not keeping water hot after hours of no hot water use, water being way too hot when it is hot, and 12+ periods of it seeming to try and refill after using a large amount of hot water.”source ↗
“Recently, the issues have become much more frequent, leaving our water cold more often than it is hot.”source ↗
“My water heater has finally failed, water doesn’t get hot only luke warm.”source ↗
“good replacements for under a grand?”source ↗
“i called three plumbers, the all said i needed to replace it.”source ↗
“It is an AO Smith 40 gallon model and where the anode rod should be on top next to the cold inlet port it looks like the installers put the pressure relief valve and drain pipe.”source ↗
“My question is am I seeing this correctly? How could a water heater be installed by a major gas company without the anode rod and if so, how badly am I in trouble?”source ↗
“Put a bucket under there and shut the water and gas off to the unit.”source ↗
“Got new water heater 5 years ago. Noticed this corroded spot and water drips this morning.”source ↗
“I think it’s coming from underneath the unit…”source ↗
“Pretty sure it’s coming from underneath the unit”source ↗
“I moved into my house 4 years ago and didn't realize that I needed to descale.”source ↗
“I called a plumber to check it out, and they said I need to replace the unit since I haven't done any maintenance.”source ↗
“They said if I descale it, my unit will just break.”source ↗
“I need some expert opinions.”source ↗
“I've got a slow drip coming from the piping you see here. Am I definitely going to have to replace the T&P valve or is there some other remedy?”source ↗
“Last Sunday my T&P valve broke and water started rushing like a faucet out of it.”source ↗
“everything was fine, 6 days later it started dripping 3 or 4 drops a second.”source ↗
“Not really sure what I should do now and if I I just need a new water heater or maybe try another valve”source ↗
“I just moved into this apartment a week ago and just noticed that the bottom of the water heater is all rusted. Is it a problem I should address immediately?”source ↗
“I don't know much about water heaters internal structure so i want to know whether the rusting of this part could mean severe internal decay and should i be worried about it breaking/leaking soon.”source ↗
“My confusion is that the female is tied into the pex so when I start twisting that off, it will move the pipe with it. No?”source ↗
“Last year she said the breakers started tripping on both of them, and she’s just been turning them back on.”source ↗
“About a month ago a very strong sulfur smell started emanating from the water.”source ↗
“She said she’s never had them maintenanced over the past six years. It’s clear the anode rods are totally shot.”source ↗
“Noticed this small amount of water coming from the bottom of the water heater.”source ↗
“Since its not the TandP valve, I'm gonna say the tank is done. You're sure its not a pipe up top leaking and running down?”source ↗
“Just had this happen to me over the weekend. Small leak on Wednesday and I thought "eh, seems like a weekend problem" and just throw a Tupperware container under it.”source ↗
“Difficult to say for sure. Leak doesn't appear to be originating from any of the visible plumbing. Very small amount of water at the base of the tank on the other side. Sounds like the tank itself, any ideas on how urgent this is to get replaced?”source ↗
“It is dripping from this uncapped pipe. Any ideas what this is? I can't disprove that the tank is leaking, but i got this pipe dripping on video.”source ↗
“we'd been living with crusty flow for months without realizing it.”source ↗
“Would you let it ride or try to flush and replace rod?”source ↗
“My parents had a tank that was going on 12 years with zero maintenance, never flushed, anode was just a sad little wire when we finally pulled it. Dad decided to flush it and the thing started leaking within a week.”source ↗
“I had a 20yr old tank that wasn’t being maintained, sprung a leak 4 years into ownership because I wasn’t aware anode rods are a thing.”source ↗
Where this came up
People with this problem also raised
- 7Can I replace a hot water heater with a direct swap if ports match?
- 3Do I need a plumber for rusted water heater connections?
- 3Why is my water softener bubbly and need cleaning?
- 3Why does only the hot water smell like sulfur after moving in?
- 14Why is there water on the floor around my new water heater?
- 6Why does a new water heater require so many infrastructure upgrades?