One homeowner's attempt to solve a strange plumbing issue drew a quick reality check online.
When the cold water tap was turned on, warm water came out for about fifteen seconds before cooler water started flowing. Because of this, the resident turned to Reddit's r/Plumbing community to ask whether an expansion tank would fix the problem.
Here's what to know
In the Reddit thread, the homeowner in a two-person household described a brief warm-water surge coming from the cold side of several fixtures. The pattern appeared after long periods without hot-water use and affected bathroom sinks, showers, the utility sink, and the kitchen faucet.
The original poster added, "I'm pretty confident that adding an expansion tank to the hot water heater will resolve this issue. My question is, if I can live with this issue, do I have to install the expansion tank? Am I unknowingly doing some damage somehow?"
To the OP's surprise, commenters told them not to expect an expansion tank to fix a short burst of warm water from the cold side. Their consensus was that the tank could still matter for the plumbing system, just not for that specific symptom.
One wrote, "Having the expansion tank won't fix that, but you should always have one anytime you're on a closed plumbing system, which you likely are."
Another commenter explained, "You are getting cold water from somewhere where your pipe cools, then warm water left in the pipe from a crawl space maybe, then finally cold water from outside."
The same user added, "Most code and most home plumbing situations require an expansion tank these days so no harm in adding one, they prevent damage, so don't worry there. But one won't fix your temp issues."
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More background
As the comments section noted, an expansion tank may not solve a fixture-temperature issue if the cause is pipe routing or a crossover between hot and cold lines.
And buying the wrong part can waste money while leaving the original issue untouched. Even if an expansion tank does nothing for the brief burst of warm water, it may still be important for pressure control on a closed plumbing system.
Before adding equipment, commenters urged the homeowner to narrow down the cause of the temperature swing. One commenter asked whether the water would eventually turn hot if left running, while another pointed to a leaking single-handle shower or faucet valve that could be mixing hot and cold internally.
If the discussion leads a homeowner toward replacing the water heater itself, Cala makes smart heat pump water heaters. Cala's customizable smart heat pump water heaters can help homeowners lower energy bills by heating water exactly when they need it. For households weighing a replacement anyway, Cala offers a way to pair water-heating performance with lower operating costs.
Where can I learn more?
For more on the water heater and plumbing issues that came up here, these stories cover debates about expansion tank installation.
• In Florida, a homeowner's water heater expansion tank install drew warnings to use brass.
• A homeowner questioning an upside-down expansion tank learned the unusual installation can be normal.
• Plumbers said the 'easy' expansion-tank swap needed support before a $500 repair made sense.
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