Scale on the heat exchanger. In hard water these need descaling roughly annually and most never get it. Some units can be flushed by the owner if isolation valves were installed; many were not.

This is most common in homes built since 2000. PEX on slab, 200 amp service, builder-grade equipment that reaches end of life across a whole street at once.

Related

• Pressure drops at every fixture at once
• Every drain in the house is slow, not just one
• Rusty water only on the first draw
• The main shutoff will not turn
• Sewer backs up in the lowest fixture after heavy rain
• Sewer smell from a room nobody uses
• Hose bib with no vacuum breaker
• Stain on the ceiling directly under a bath

Back to Plumbing.

---

Written by Jaylan Jones. I Like To Fix earns a referral fee when a call connects to a contractor. See our business-model disclosure.