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I have a Rinnai R85 tankless water heater. We recently had an issue with no hot water which was resolved by performing a flush. Since then, upstairs sinks and tubs are fine, but our two kitchen sinks have no pressure and one doesn’t have pressure on hot or cold. HELP!!! Nothing was changed on any lines - but there’s no pressure and only in those sinks.

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An issue with no hot water being resolved by performing a flush suggests to me that there was a buildup -- hard water scale, ie mineral deposits -- on the inside of the heat exchanger tubing. I suspect that the deposits were not entirely removed from the heater during the flush. Some debris may have remained inside the plumbing. That debris found its way to some faucets and is now plugging them.

The first thing to check is the aerator. This is a screen assembly installed right at the point where water comes out. Unscrew it and clean out any debris. It may not be easy to remove, especially considering that you had scale problems in the water heater.. Soaking the end of the faucet in vinegar for a few hours may ease the removal.

If cleaning the aerator doesn't resolve the problem the next thing to check is the faucet valve. Remove it, check for damage or debris, and re-install.

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  • Since I posted this, I checked the aerators. Nope. Slight sediment, but nothing blocking and easily cleaned off. Decided to do a backflush. Cold water shutoff valve shut the water off fine - but hot shutoff valve doesn’t. I have a feeling that the shutoff valve is where the sediment/issue may lie. Unfortunately, I have no idea how to resolve that other than shutting off the main water supply and attempting to take it off. But that doesn’t quite explain why there’s no HOT water coming out if that valve won’t close. – Dee Majeski Jun 1 '20 at 23:45
  • It is possible the hot water shutoff broke in an intermediate position. Therefore being half open it is both restricting the flow and won't move to close off the water. – mfarver Jun 2 '20 at 15:25
  • If upstairs bath and sinks flow hot water fine but the kitchen fixtures don't at all then there must be trouble in some component that affects only the kitchen. If the shutoff valve at the heater doesn't work that's a separate problem -- if that were blocking flow it would affect the baths as well. To diagnose the no-flow problem in the kitchen you'll have to start disassembling. I'd probably remove the stop valve from the wall/floor piping below the sink and check for flow and debris there. Depending on the outcome, look deeper into the building plumbing or the kitchen faucet and valves. – Greg Hill Jun 2 '20 at 17:21

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