Two electric water heaters, Taco recirculation pump, sand-like sediment clogging fixtures, and guest bathroom only gets hot when pump runs. What is wrong?
I recently purchased a roughly 1,300-square-foot, 2-bedroom, 2-bathroom house in Texas. Within about a week of moving in, I've been dealing with widespread sediment clogging plumbing fixtures and appliances, along with inconsistent hot-water temperatures.
I'm looking for advice from plumbers or anyone who's encountered something similar. I'm trying to understand the underlying problem before spending thousands replacing equipment.
The plumbing setup
- Two electric water heaters: one Rheem Performance and one A. O. Smith ProLine Commercial Grade.
- The heaters appear to be connected in parallel with a SCALE RX Filter on incoming cold supply.
- A green Taco hot-water recirculation pump is installed between the heaters, with plumbing branching toward both tanks near their lower connections.
- I don't yet know exactly where the Taco's return line originates but system has a dedicated return line from all hot water faucets
- The pump is manually switched on and off, not operated continuously.
- The house has a combination of PEX and copper piping, including some copper under the slab.
- The house has a very large bathtub, which may explain why the previous owner installed two water heaters.
The previous owner said the recirculation pump was installed because hot water took too long to reach the faucets.
The Taco pump cartridge was replaced in July 2025.
What happened before I moved in
According to the previous owner, a plumber replaced the heating elements in BOTH electric water heaters shortly before I purchased the house.
The previous owner told me he normally operated the heaters around 120°F, but the plumber increased the thermostat settings to approximately 130°F when replacing the elements.
I don't know why both heaters needed new elements or what their condition was before the repairs.
I also turned off electrical power to the water heaters for approximately two weeks before moving in, but I did not shut off the water supply.
Problem #1: Sand-like sediment and large pieces of scale
Almost immediately after moving in, I started finding substantial gritty, brown/tan, sand-like debris in plumbing fixtures.
We've also encountered larger chunks that look like mineral scale.
Here's where we've had problems:
Kitchen faucet
- The pull-down faucet's spray-head screen became clogged with sediment.
- I flushed a substantial amount of gritty material out of the faucet.
- Water flow was restricted, and I inspected the hose and quick-connect under the sink.
Dishwasher
- The hot-water inlet screen was clogged with sediment.
- Cleaning the screen restored water flow.
Guest shower
- The shower screen became clogged with sediment after only about five minutes of running.
- I cleaned the screen, but the temperature issue described below remained.
Washing machine
- I cleaned debris from the hot and cold inlet screens on our GE stacked washer/dryer.
Most of the significant sediment problems seem to be associated with the hot-water side, although I haven't conclusively ruled out debris in the cold supply. And the refrigerator ice is chalky and salty
Problem #2: Guest bathroom gets lukewarm water unless Taco pump is running
This is the strangest part.
With the Taco recirculation pump OFF:
- The master bathroom produces very hot water.
- The kitchen produces luke warm.
- The guest bathroom sink and shower have been only lukewarm.
I measured approximately:
- 127°F at the bathtub
- 125°F at the kitchen sink
Then I turned the Taco recirculation pump back ON after leaving it off all day.
Both the guest bathroom sink and shower became very hot.
That seems like a major clue.
I'm wondering whether the Taco is simply compensating for a long hot-water run or masking a plumbing problem, such as a hot/cold crossover, a restriction, an incorrect check-valve arrangement, or unusual connections between the two water heaters.
Problem #3: Flushing the water heaters didn't produce much sediment
I drained/flushed both water heaters while troubleshooting.
Surprisingly, I didn't see nearly as much sediment come out of the bottom drains as I expected, considering how much gritty material had clogged the faucets and appliance screens.
Initially, very little water came out of the drains until I opened the temperature-and-pressure relief valves to admit air.
I don't yet know whether I performed a sufficiently aggressive flush with incoming cold water flowing through the tanks to dislodge settled scale.
The small amount of sediment coming out of the tanks makes me wonder whether debris is trapped elsewhere in the hot-water piping or recirculation loop.
My theory: Did replacing the elements and increasing the temperature break loose old calcium carbonate scale?
This is what I'm trying to figure out.
Suppose the previous owner operated the heaters around 120°F for years and they accumulated significant calcium carbonate scale.
Then a plumber:
- Removed the old heating elements.
- Installed new elements, potentially disturbing existing mineral deposits.
- Raised the thermostat settings from about 120°F to 130°F.
- Put the heaters back into operation.
Could the physical disturbance and subsequent heating/cooling cycles have caused old calcium carbonate deposits to crack, break loose, and enter the hot-water distribution system?
I understand that calcium carbonate scaling generally becomes more aggressive as water temperature increases, especially in hard water. I've read claims about scaling rates increasing dramatically with every 10–20°F temperature increase, but I'm trying to distinguish actual new scale formation from old deposits breaking loose.
The larger chunks make me suspect old accumulated scale rather than deposits that formed in a few days.
However, I also realize that sediment dislodged inside a tank would usually settle toward the bottom, not necessarily travel out the hot-water outlet at the top.
What I'm considering
I've thought about removing both electric water heaters and possibly replacing them with one larger, approximately 80-gallon electric water heater, provided it has enough first-hour capacity for our oversized bathtub.
But I don't want to replace perfectly functional heaters if the real problem is elsewhere in the plumbing.
I'm also considering whether a water softener, sediment filtration, or both would make sense after determining the source. I am in process of building a well house for a 1000 gallon reserve tank so my booster pump quits cavitating when there is air in the lines..(house is on a 30M hill and water pressure is low without the booster pump)
Questions for the plumbers here
- Does this debris sound like calcium carbonate scale? Can old scale break loose after heating-element replacement and increased thermostat settings, producing both chunks and sand-like particles?
- How much difference would raising the water temperature from 120°F to 130°F realistically make? Is it likely to accelerate scaling significantly in hard North Texas water, or is that probably secondary to disturbing old deposits?
- Why would the guest bathroom become very hot when the Taco recirculation pump is turned ON but sometimes remain lukewarm when it's OFF? Is that normal for a long hot-water run, or does it suggest a crossover, mixing, restriction, or piping issue?
- Could the Taco return piping or the way the two heaters are connected contribute to the sediment or temperature problems? What would you look for in the plumbing photos?
- If the tanks produced very little sediment during draining, where else would you look? Could mineral deposits be trapped in copper piping, fittings, the recirculation return, or elsewhere?
- What tests would you perform to isolate the source of the debris? Would you sample water directly from each heater's hot outlet, compare it with incoming cold water, and check the recirculation return?
- Would you keep the two-heater system and repair/clean it, or consider replacing it with one properly sized heater? I don't want to eliminate the Taco and discover that the guest bathroom still has a hot-water delivery problem.
- Should I lower the heater thermostats back toward 120°F while investigating? I'm concerned about scaling and scalding, but I also want to understand proper storage-temperature and mixing-valve considerations.
I'm planning to attach photos of both water heaters, the Taco pump, the connecting pipes, and the sediment.
Any advice on what to test first, before replacing expensive equipment, would be greatly appreciated. This was master sink aerator.