Tankless water heater won't flow when trying to descale
When following a tutorial to descale the heater yourself, the water sometimes fails to pass through the unit. Instead of circulating and coming out the hot water side into the bucket, the flow simply stops.
Overview
People affected2 accounts across 1 forum
Workarounds found6 items attempted
Community agreement3 total upvotes
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
6 items+ Contribute
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Trying different valve hookups such as the main header or three-way valvesDid this help you?
- 2Back flushingDid this help you?
- 3Toggling unit power and plug statusDid this help you?
- 4Opening the smaller service valves near the hose connections.Did this help you?
- 5Putting the water heater into service mode so it allows flow.Did this help you?
- 6Running the hot water faucet and unplugging the unit while it is still running to bypass flow restrictions.Did this help you?
Tried another approach not listed above?+ Share your workaround ↑
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
r/Plumbing2 people · October 2026 – November 2026
“Trying to descale my tankless water heater myself and followed a tutorial but the water is not going through the heater and coming out of the hot water side into the bucket.”source ↗
elin_78 · r/Plumbing · 5 upvotes
Where this came up
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